the correct question is
What is the value of x in the following equation (1/5)^x=5^8
Applying logarithms both members
log(1/5)^x=log(5^8)
x*log(1/5)=8*log(5)
x=8*log(5)/log(1/5)
we know that
log (1/5)----> log (1)-log (5)----> 0-log (5)-----> -log (5)
so
x=8*log(5)/-log (5)------> x=-8
the answer is
-8