A river is flowing at the rate of 2.4 miles per hour when a girl rows across it. If the girl rows at a still-water speed of 3.1 miles per hour and heads the boat perpendicular to the direction of the current, what is the resulting speed of the boat?
a)1.09
b)0.447
c)2.45
d) 3.92
The answer is 3.92
