I think it is done like this but I am not sure.
Simplifying
9 + -4(2x + -1) = 45
Reorder the terms:
9 + -4(-1 + 2x) = 45
9 + (-1 * -4 + 2x * -4) = 45
9 + (4 + -8x) = 45
Combine like terms: 9 + 4 = 13
13 + -8x = 45
Solving
13 + -8x = 45
Solving for variable 'x'.
Move all terms containing x to the left, all other terms to the right.
Add '-13' to each side of the equation.
13 + -13 + -8x = 45 + -13
Combine like terms: 13 + -13 = 0
0 + -8x = 45 + -13
-8x = 45 + -13
Combine like terms: 45 + -13 = 32
-8x = 32
Divide each side by '-8'.
x = -4
Simplifying
x = -4
