Solve 2^x=20 express the awnser as a calculator ready expression
log(20) divided by log(2) = x
rewrite in log form
2^x = 20 …
log base 2 of 20 equals x
you can find a log on calculators that dont allow you to enter a base.
log base 2 of 20 = log20 divided by log2
(using the standard 10 base)