8(x+15)-20=10x
8x+8×15-20=10x
10x-8x=120-20
2x=100
x=100÷2
x=50
2(100-x)-15=150-x
2×100-2x-15=150-x
2x-x=200-15-150
x=35
25x-165=10(15-x)
25x-165=10×15-10x
25x+10x=150+165
35x=315
x=315÷35
x=9
5(x-10)=3x-6
5x-5×10=3x-6
5x-3x=50-6
2x=44
x=44÷2
x=22