Question 1046197
Let x be the rowing speed of the crew. Then:
9/(x+1)+9/(x-1)=3.75
9(x-1)+9(x+1)=3.75x²-3.75
36x-36+36x+36=15x²-15
15x²-72x-15=0
(15x+3)(x-5)=0
x=-3/15,5
Throwing out the negative result, the rowing speed of the crew in still water was 5 kph. ☺☺☺☺