Use a log identity such as log(x)-log(y)=log(x/y), x,y>0. The given equation can be written as follows:
log(3^5)-log(3^8)=log((3^5)/(3^8)) ··· Eq.1
Use an exponent rule such as (a^m)/(a^n)=a^(m-n), a(≠0),m,n: any real numbers. Eq.1 can be rewritten as follows:
log((3^5)/(3^8))=log(3^(5-8))=log(3^-3)
The answer is: log(3^5)-log(3^8)=log(3^-3) (=-3log3)