Connie's boat travels at 77 mph. find the rate of the current of the river if she can travel 1515 miles upstream in the same time she can travel 2727 miles downstream.

I assume 1515 should be 15 and 2727 should be 27.
If the speed of the current is c this reduces the upstream effective speed: 77-c and increases the downstream effective speed: 77+c.
Time=distance/speed=15/(77-c)=27/(77+c).
15(77+c)=27(77-c).
1155+15c=2079-27c.
42c=924, c=22mph.

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