Question

800 - (y*8-20) = 100

Answer 1

800 - (8у - 20) = 100
800 - 100 = 8у - 20
700 = 8у - 20
8у = 700 + 20
8у = 720
у = 720 :8
у = 90

Answer 2

800-(y•8-20)=100
y•8-20=800-100
y•8-20=700
y•8=700+20
y•8=720
y=720:8
y=90
—————————
800-(90•8-20)=100
100=100