The answer is the option C and the option D, which are:
C. Double the number of pages in the book.
D. The age of my friend.
The explanation for this problem is shown below:
By definition, a variable is an unkown quantity. In the Option A the quantity is given: 
seconds in a minute. In the option B you know the quantity too, which is 
years old. But the option C and the option D does not give any quantity, you don't know the number of pages in the book or the age of the friend yet. Therefore, the answer is the options C and D.
Answer:
A. Use the distributive property.
Step-by-step explanation:
We cannot use the distribute property because there are not parentheses to distribute a number through.
5x + 15 + 2x = 24 + 4x
We can collect the terms, and isolate the variable
Answer:
<h2><u>440 ft.²</u></h2>
Step-by-step explanation:
Surface area of the object = 2 (lw + wh + hl) = 2 (10× 6 + 6 × 10 + 10 × 10)
= 2 ( 60 + 60 + 100) = 2 × 220 = 440 ft.²
Answer: 56
Step-by-step explanation:
