A=4 because 8x-8+3ax= 5ax-2a
(8+3a)x-8 =(5a)x - 2a
Subtract both sides by 5ax
(8+3a-5a)x - 8= -2a
Now add both sides by 8
(8-2a)x=8-2a
Notice that the coefficient of x in the left side is the same as the constant on the right side.
For equation to be true, no matter what value of x, 8-2a must be 0
Set 8-2a equal to 0
8-2a equal to 0
8= 2a
a= 4