Logarithm problem, teach me how to fo, thanks?

(a)
y=ab^x
log3(y)=log3(ab^x)
=log3(a)+log3(b^x) [log(ab)=log(a)+log(b)]
=log3(a)+x*log3(b) [log(a^2)=2*log(a)]
(b)
when log3(y)=4 , x=0
4=log3(a)+0*log3(b)
=log3(a)
a=81
when x=2 , log3(y)=0
0=log3(a)+2*log3(b)
=4+2*log3(b)
-2=log3(b)
b=1/9