9*(х-5)+4*(6-х)=3+3*(х+20)-2х
Решение

9 * (x - 5) + 4 * (6 - x) = 3 + 3 * (x + 20) - 2x
9x - 45 + 24 - 4x = 3 + 3x + 60 - 2x
5x - 3x + 2x = 3 + 60 + 45 - 24
4x = 84
x = 84 / 4 
x = 21