Apply the function inverse to log to both sides.
The inverse of is - that is if then . Your problem is a little ambiguous because you do not give a base for the logarithm. Normally, that would imply the "common logarithm", base 10. If that is the base here, then . That is probably correct here but in higher level mathematics it is common to use "log" rather than "ln" to mean the natural logarithm. If that is the case, then .