a)3x+12
x-y=1
x=12÷3
x=4
4-y=1
-y=1-4
-y=-3/x-1
y=3
b) 5y=2
x=y=2 2/5
x=2 2/5
y=2 2/5
c)4y-x=6
17y=0
y=0÷17
y=0
4x0-x=6
-x=6
x=-6
d)a=b
2a+b=9
b=9-2a
a=9-2a
a +2a=9
3a=9
a=3
b=3
e)u=4v
5u-v=10
5x4v - v=10
20v-v=10
19v=10
v=10/19
u=4 x 10/19
u=40/19
u=2 i 2/19
f) 3r=s
3r+s=24
3r+3r=24
6r=24
r=3
s=3 x3
s=9