X miles per hour - <span> speed of the boat in still water
(x - 2) - speed up the river
(x + 2) - speed down the river
</span>

=

30 * (x + 2) = 38 * (x - 2)
30x + 60 = 38x - 76
- 8x = - 136
x =
17 miles per hour - <span>
the speed of the boat in still water.</span>
V= pi x r^2 x h
V/(pi x h)=r^2
square root of [V/(pixh)]=r
5x - 15 = 50
Add 15 to both sides
5x = 65
Divide both sides by 5
x = 13
Hope this helped :)