Question 1056082
v1*t1=distance
(x-3)*t1=4
t1=4/(x-3)
v2*t1=10
(x+3)*t1=10
t1=10/(x+3)
set the two times, which are the same, equal to each other.
4/(x-3)=10/(x+3)
Cross-multiply
10x-30=4x+12
6x=42
x=7 mph ANSWER
downstream at 10 mph, counting current, and it takes him 1 hour to do 10 miles
upstream at 4 mph, counting current, and it takes him 1 hour to do 4 miles.