1) 21(x-6)=20(x+1)-36(x+2)
21x-126=20x+20-36x-72
21x-20x+36x=126-52
37x=74
x=2
2) 18(x-8)+35(x+5)=8(7x+1.5)+10
18x-144+35x+175=56x+12+10
53x+31=56x+22
31-22=56x-53x
3x=9
x=3
3) 9(2x+5)-16(5x+7)=42(x-15)-165
18x+45-80x-112=42x-630-165
18x-80x-42x=-630-165+112-45
-104x=-728
x=7