Algebra
posted by Amber .
on a canoe trip, Rita paddled upstream (against the current) at an average speed of 2 mi/hr relative to the riverbank. on the return trip downstream (with the current), her average speed was 3 mi/hr. find rita's paddling speed in still water and the speed of the river's current.
dealing w/ substitution and elimination

let w be the water speed
let b be the boat speed in still water.
bw=2
b+w=3
solve. I would add the two equations to eliminate w. 
bw=2
b+w=3 (transpose)
b=3w (substitute)
3ww=2 (combine like terms)
2w=1 (cancel 2)
w= 1/2