Jens boat cruised 45 miles upstream and 45 miles back in a t

Jen\'s boat cruised 45 miles upstream and 45 miles back in a total of 6 hrs. The speed of the river is 2 mph. Find the speed of the boat in still water.

Solution

[45 / (b-2)] + [45 / (b+2)] = 6

multiplying by (b-2)(b+2) ___ 45b + 90 + 45b - 90 = 6b^2 - 24

0 = 6b^2 - 90b - 24

dividing by 6 ___ 0 = b^2 - 15b - 4

use quadratic formula to find b