I need math help plz

Question

 You paddle 2 miles downstream in a canoe at a rate of r + 3 miles per hour. You turn around and paddle 1 mile upstream at a rate of 0.75r miles per hour. You then return to your original starting point at a rate of r miles per hour. Write a model in simplified form for the total time t (in hours) of the trip. t=a/3r(r+3) How long does your trip take when r is 2 miles per hour?

Answer 1

distance = rate of speed times time

d=rt

time = distance divided by rate of speed

t = d/r

t = 2/(r+3) + 1/r + 1/(3r/4)

= (13r +21)/3r(r+3

for r=2

t = (13(2)+21)/3(2)(2+3) = 47/30 = 94/60 = 1 hour and 34 minutes for the full trip and back, total 4 miles