To solve for x, you need to isolate/get the variable "x" by itself in the equation:
10(x - 2) = -20 Divide 10 on both sides

x - 2 = -2 Add 2 on both sides to get "x" by itself
x - 2 + 2 = -2 + 2
x = 0
PROOF
10(x - 2) = -20 Substitute/plug in 0 into "x" since x = 0
10(0 - 2) = -20
10(-2) = -20
-20 = -20