How am I supposed to simplify this logarithm? Given is $$\log_6(a)=6$$
Simplify - $$\log_6 (1/a^7)$$ and the answer is supposed to be $-42$. 
I don't understand what I'm supposed to do here?

HINT
Recall that by definition
$$\log_6a=6 \iff 6^6=a$$
then
$$\log_6\left(\frac1{a^7}\right)=x \iff 6^x=\frac1{a^7}$$
or use that


*

*$\log x^n=n\log x$

*$\log \frac1x=-\log x$
