The sum of 7 and 5 is 12. This basic addition problem reinforces fundamental arithmetic skills.

Option C is grammatically correct because it properly uses the present perfect tense. It also demonstrates correct subject-verb agreement.

Multiplying 9 by 3 gives 27. This reinforces basic multiplication skills.

Asia is the largest continent by land area. This basic geography question tests knowledge of the world's continents.

Water is typically found in a liquid state at room temperature. This question assesses understanding of basic states of matter.

The order of operations requires solving the expression inside the parentheses first, then performing multiplication followed by addition. Therefore, 2 + 3 x 2 equals 8.

The word 'quickly' describes the manner in which the action was performed, modifying the verb 'finished.' This makes it an adverb in the sentence.

Among the options provided, 'big' is synonymous with 'large.' This question tests vocabulary by requiring the identification of equivalent words.

The area of a rectangle is determined by multiplying its length by its width, which in this case is 10 x 4 = 40. This reinforces the fundamental concept of area calculation.

Mars is commonly referred to as the Red Planet due to its reddish appearance caused by iron oxide. This question tests basic astronomical knowledge.

Option B is punctuated correctly because the comma properly distinguishes the vocative 'grandma' from the rest of the sentence. This increases clarity in written communication.

By dividing both the numerator and the denominator by their greatest common divisor, 5, the fraction 10/15 simplifies to 2/3. This tests the ability to simplify fractions.

Gravity is the force of attraction between masses and is responsible for keeping planets in orbit around the sun. This concept is essential to understanding astronomical mechanics.

Japan is known as the 'Land of the Rising Sun' due to its location in the east and historical references in its culture. This question assesses geographical and cultural knowledge.

George Washington served as the first President of the United States after the nation's founding. This historical fact is essential background knowledge in American history.

First, determine the cost per pencil by dividing $3 by 5, resulting in $0.60 per pencil. Then, dividing $18 by $0.60 shows that you can buy 30 pencils, demonstrating proportional reasoning.

Apply the distributive property to both sides to get 3x - 6 = 2x + 8, then subtract 2x from both sides and add 6 to isolate x, yielding x = 14. This problem tests skills in solving linear equations.

The phrase 'who had a reputation for fairness' is set off by commas and provides additional, non-essential information, making it a non-restrictive clause. This tests understanding of complex sentence structure in language arts.

The pyramids of Egypt were constructed by the ancient Egyptians as monumental tombs. This question tests historical knowledge of ancient civilizations and their architectural achievements.

Increasing the length by 20% multiplies it by 1.2 and decreasing the width by 10% multiplies it by 0.9; multiplying these factors gives 1.08, which reflects an 8% increase in area. This problem requires an understanding of percentage changes in dimensions and area calculations.