Answer :
b=a+6
b+a=42
susitute
a+6+a=42
subtract 6
2a=36
divide 2
a=18
subisute
b=18+6=24
b=24
a=18
b+a=42
susitute
a+6+a=42
subtract 6
2a=36
divide 2
a=18
subisute
b=18+6=24
b=24
a=18