Can someone help me with this?

Let x represent the speed of the boat in still water.

time = distance/speed
time downstream = time upstream
96/(x +4) = 48/(x -4) . . . . . fill in the given information
2(x -4) = x +4 . . . . . . . . . . . multiply by (x-4)(x+4)/48
2x -8 = x +4 . . . . . . . . . . . . eliminate parentheses
x = 12 . . . . . . . . . . . . . . . . . add 8-x

The speed of the boat in still water is 12 mph.