Answer:
7
Step-by-step explanation:
-3 + 3 = 0
0 + 4 = 4
4 + 3 = 7
The first is a. you can rewrite it

the second is d. the only common factor between 20 and 40 that can be taken out is the 4 which becomes a 2, but inside the square roots there is still a 5 and 10, which cannot be combined
the third is c.

the fourth is d.
add 3 to both sides

then square both sides

then divide both sides by 2, x=50
The answer is 
First, you must divide 12 on both sides.

Then, simplify the fraction.

I am the diffrence of the two numbers... sum is 36 so the larger is double the size of the smaller the only numbers that work are 24 and 12 so the diffrence would be 12