(15-10y)-(36-4y)=3y+15
15-36-10+4y=3y+15
-21-6y=3y+15
-6y-3y=15+21
-9y=36
y=36/(-9)
y=-4
28x-42-5x-20=6x+10+5x
23x-62=11x+10
23x=11x+72
23x-11x=72
12x=72
x=72/12
x=6
(27x-63)+(24x-33)=27x+24
51x-96=27x+24
51x-27x=24+96
24x=120
x=120/24
x=5
42x-66-13x+78=28x+14
29x+12=28x+14
29x-28x=14-12
x=2