math
posted by sam on .
A boat's crew rowed 12 miles downstream, with the current, in 1.5 hours. The return trip upstream, against the current covered the same distance, but took 4 hours. Find the crew's rowing rate in still water and the rate of the current...
The crew's rowing rate in still water is ??? mile(s) per hours.
The rate of the currents is ??? mile(s) per hour.
Please HELP, this question is hard, and I don't understand it.

Let the rowing rate be x mph
let the current's rate by y mph
going with the current, will be a rate of x+y mph
going against the current would be xy mph
so you get two equations, using Distance = rate x time
1.5(x+y) = 12
4(xy) = 12
1st: divide by 1.5
> x+y = 8
2nd: divide by 4
> xy = 3
add them
2x = 11
x = 5.5 mph
back in 1st, y = 2.5 mph
so the rowing speed is 5.5 mph,
the current's speed is 2.5 mph