I think when you have a fraction like that, you multiply the denominator on both sides obviously by the first step
1 - 3x/5 = -7
Multiply on both sides
1 - 3x/5 * 5 = -7 * 5
and Solve
1 - 3x = -35
Subtract 1 from both sides of the equation
-3x = -36
Divide both sides by -3
-3x / -3 = -36 / -3 (← answer)
x = 12
Hope it helps