Question

Eight times the difference of a number and seventeen is thirty"?

Answer 1

difference of a number and 17: x - 17
eight times that = 8(x - 17)
8(x - 17) = 30

divide both sides by 8
x - 17 = 30/8

x = 30/8 + 17 which is 20.75

Answer 2

Let the number be y;
8*(17-y)=30
8*17-8y=30
136-8y=30
-8y=30-136
-8y=-106
y=-106/=8
y=53/4