no logarithms needed here, just some "simple" simplification

you seem to be on the money so far. i will restart the problem though. you way is fine, but it seems having the halves around was confusing you. i will rewrite the problem using powers of 2, not 1/2

....................(1)

.....................(2)

equating (1) and (2), we obtain:

back-substitute into (1):

if you insist on picking up where you left off:

.........divide both sides by 5...

............multiply both sides by

and the rest is trivial