You have to take the inverse of log, that is ...
what number d you you need, so that log d = .989...
BTW, I got log d = 1.9892....
hope yours was just a typo.
On most calculators, use the 2ndF key
on mine, I would press the following:
2ndF
log
1.98924..
=
to get 97.5545
Without having to re-enter the 1.98...
Here is the sequence of my keystrokes
250
-
65
=
÷
93
=
2ndF
log
=
to get the 97.5545