You need to know the z-score associated with the 73rd percentile. Do you have a chart or table? Are you using a percentile to z-score calculator? Depending on the method you use, you will find that the appropriate z-score is 0.6128 (or something close, depending on the number of significant figures your table or chart uses). So, how do you find a z-score.
So, plug in the values you know:
to find the 73rd percentile salary for male professors and
to find the 73rd percentile salary for female professors.
In each case, solve for