There is actually 2 ways to solve this, I will show you both.
The first is obvious, solve for x in the first one, and plug it into the 2nd one and get the answer
4x + 7 = 12
4x = 5
x = 
8(
) + 3
2 * 5 + 3
10 + 3
13
The 2nd option is to manipulate the 4x + 7 to be 8x + 3
4x + 7 = 12
start by moving the 7 over
4x = 5
multiply both sides by 2
8x = 10
and add 3 to both sides
8x + 3 = 13
70% I think beacuse she is making more profit about 70% then she bought it for
BANK A:
5,000*0.03*5=750
BANK B:
5,000*0.025*6=750
They are the same

so if x = -1, let's plug that in the second equation
-5(-1)+y = 5
5+y = 5
y = 0
I think -16 that's what I think I hope it helps