algebra word problem
posted by christy on .
During the first part of a trip a canoeist travels 55 miles at a certain speed the canoeist travels 15miles on the second part of the trip, 5 miles per hour slower. The total time for the trip is 4hours. What was the speed on each part of the trip.
This is what I have so far, then I am lost
t1= 55/r t2=15/r5 =4
r (r5) (55/r + 15/r5) =4
55 (r5) +15r=4r (r5)
55r275 + 15r=4r^220r
Now I am lost.

You are practically there!
Combine terms and rearrange to get into the form:
4r^2 90r + 275 = 0
Use the quadratic formula to find r. There will be two answers. One of the answers is the result if the canoeist reverses direction (r5 is negative). 
r5 being negative results in a negative t2 and so should be ignored.