I need help figuring out a distance=rate times time problem?

Question

On a weekend outing, Antoine rents a motorboat for 8hr to travel down the river and back. The rental operator tells him to go for 3hr downstream, leaving him 5hr to return upstream.
a)If the river current flows at a speed of 6mph, how fast must Antoine travel in order to return in 8hr.
b)How far downstream did Antoine travel before he turned back?

Answer 1

Rate downstream: r+6
Upstream: r-6

3(r+6)=5(r-6

3r+18 = 5r-30

48 = 2r

r = 24

24 mph ir the required speed for Antoine

b. Distance downstream was 3(r+6) = 3(24+6) = 90 miles

Answer 2

let r= speed of the boat:
r+6 = rate going downstream
r-6 = rate going upstream.
d = (r+6)*3 = (r-6)*5
a)
3r+3*6=5r-5*6
2r = 3*6+5*6
r = 6*(3+5)/2

b)
d = 3*(6(3+5)/2+6)