2.
2x+y=10
x-y=2 => y=x-2
2x+x-2=10
3x=12
x=4 => y=4-2=2
sol x=4
y=2
3.
a+b=48
a=4b+3
=> 4b+3+b=48
5b=45
b=9 => a=48-9=39
sol a=39
b=9