s=sullivan's age
d=daughter's age
in 3 years time (s+3 and d+3)
sulivan is 3 times as old as daughter
s+3=3(d+3)
6 years ago (s-6 and d-6)
he was 6 times as old
s-6=6(d-6)
expand
s+3=3d+9
s-6=6d-36
for 2nd equation, add 6 to both sides
s=6d-30
sub 6d+30 for s in other equation
6d-30+3=3d+9
6d-27=3d+9
minus 3d both sides
3d-27=9
add 27 both sides
3d=36
divide both sides by 3
d=12
sub back
s=6d-30
s=6(12)-30
s=72-30
s=42
Mr. Sullivan is 42 now
Daughter is 12 now
