Boat trip question

[chrisw]

A boat makes a round trip, traveling dowsream first, and then upsream. It takes the boat 5 hours traveling downstream and 7.5 hours traveling upstream. If the boat travels a total of 300 miles roundtrip, find the speed of the boat and the speed of the current.

I know to use R*T=D
And I don't know what to use for the rate?
Can somebody help me?
Thanks

 

[chrisw]

I have been studying all day for a big test tommorow

 

[Denis]

b = boat speed, c = current speed

downstream: 5(b + c) = 150 [1]
upstream: 7.5(b - c) = 150 [2]
[1]=[2]: 5(b + c) = 7.5(b - c)

Solve for b in terms of c (or the other way),
then substitute back in [1] or [2].