The answer should be
4.
First, simplify

to 4. Your problem should look like: 4 x 1.
Second, multiply. 4 x 1 = 4 so that is your answer.
Also, to start the equation up, make sure to add in the numbers in replace for the letters. Your problem to start with should look like:

.
Answer:
Step-by-step explanation:
perimeter of a square = 4 x length (L)
8x - 10 + 8x - 10 = 4L
rearrange the expression
8x + 8x - 10 - 10 = 4L
16x - 20 = 4L
divide both sides for L to stand alone
(16x - 20)/ 4 = 4L/4
(16x - 20)/4 = L
In looking at it I would guess it is asking which of the points is on the line? To answer that you would have to take each point an plug it into the equation and see if it is true.
3x - 7 = y
A(9,20)
3(9) - 7 = 20
27 - 7 = 20
20 = 20 True - this point is on the line
B(5,0)
3(5) - 7 = 0
15 - 7 = 0
8 = 0 False - this point is not on the line
C(3,2)
3(3) - 7 = 2
9 - 7 = 2
2 = 2 True - this point is on the line
I hope this helps