1) 21-4d=42+3d
-4d-3d=42-21
-7d=21
d=-3
2)5y-9= -81-4y
5y+4y= -81+9
9y= -72
y= -8
3) 3(c+3)+21=60
3c+9+21=60
3c+30=60
3c=30
c=10
4)24-3(a-8)=18
24-3a+24=18
48-3a=18
-3a = -30
a=10
