Question

5x+2y= 12
10x-4y= 40

Answer 1

5x+2y=12
10x-4y=40+(-2 vezes a primeira linha)

5x+2y=12
10x-10x-4y-4y=40-24
-8y=16
y=16/-8
y=-2

5x+2(-2)=12
5x-4=12
5x=16
x=16/5