hahahah, that reminds me back in year 9 when my friend sackwacked a yr7 kid coz he was spitting apple at my friend. Funny thing was a teacher was right behind us.
You just take the 5th root of both sides and you get r=2.
But if the question was 5^r = 32, you can use log.
log(5^r) = log32
r x log5 = log32
Thus, r = (log32)/(log5) approximately = 2.15338279.