Answer:
Wang Min's situation:
Boston: 151
San Francisco: 135
If Wang Min wishes to consider a similar offer in Boston, the offer should be for at least = ($25,000/135) x 151 = $27,963. Since San Francisco is "cheaper" than Boston, she should earn more money in Boston in order to consider a comparable offer.
Roger's situation:
Cleveland: 99
San Francisco: 135
If Roger wishes to consider a similar offer in Cleveland, the offer should be for at least = ($30,000/135) x 99 = $22,000. Since San Francisco is "more expensive" than Cleveland, he should earn less money in Cleveland in order to consider a comparable offer.