You have your division the wrong way around
edit: only change the log terms to a decimal for the final answer to avoid rounding errors
edit II: checking using the original equation:
im a little unsure if i have done this right , any chance that someone could look over what i have done.
if F= 50 x 2^3t
find the value of t to 3.s.f.
when F=300
Workings.
300=50x2^3t
6=2^3t
log6=log2^3t
log6=3tlog2
3t=log2/log6
3t=0.387
t=0.129
thankyou