Question 890056
r*t=d
.
r*t=500
r=500/t
((500/t)+25)*(t-1)=500
500t+25t^2-500-25t=500t Multiply each side by t.
25t^2-25t-500=0
t^2-t-20=0
(t-5)(t+4)=0
t=5 hrs
r=100 k/h going 
125 k/h returning
.
Ed