Question 311231
From a point on a river, two boats are driven in opposite directions, one at 10 miles per hour and the other at 8 miles per hour. In how many hours will they be 54 miles apart? 

When they are at a distance of 54 miles
let boat A travel x miles 
Let boat B travel y miles 
x+y=54
.
Time taken by boat A will be x/10 hours
Time taken by boat B = y/8 hours
time taken by them is the same.
x/10=y/8
8x=10y
8x-10y=0
.
10(x+y)+(8x-10y)= 10*54+0

10x+10y+8x-10y= 540
18x=540
x= 30 Boat A travels 30 miles.

To travel 30 miles Boat A will take 30/10 hours
= 3 hours.
.
check
Boat B will travel 24 miles
Time taken by boat B = 24/8
=3 hours.

After 3 hours they will be at a distance of 54 miles