Hello Be.,
Take natural log of both sides:
ln 20.9x = ln 291
0.9x * ln2 = ln 291
Then divide both sides by ln2: 0.9x = ln 291/ln2
Then divide both sides by 0.9: x = ln 291/ (0.9*ln2)
That is the exact solution. You would then plug this in your calculator.
Cheers.
Be K.
Thank you!11/23/21