GMAT Quantitative Reasoning Practice Test 3

Mike can catch 21 fish in one hour, Jim can catch 42 fish in one hour and Bob can catch $1.5\times 42=63$ fish in one hour. 40 minutes is $\frac{2}{3}$ of an hour. After $\frac{2}{3}$ hours they all caught $\left(21+42+63\right)\times \frac{2}{3}=84$ fish.
In the next $\frac{1}{3}$ hour that's left, Jim is left alone and so he can catch $\frac{1}{3}\times 42=14$ fish. The total number of fish that they caught is $84+14=98$.