Question 281104
Let the distance that boat 1 travels be d1. 
{{{d1=r1*t=6t}}}
Let the distance that boat 2 travels be d2. 
{{{d2=r2*t=5t}}}
Since both boats start at the same time, t is the same for both. 
Since both boats travel in opposite directions, the distance between them is just the sum of their distances from the starting point.
{{{ d=d1+d2}}}
{{{d=r1*t+r2*t=6t+5t=55}}}
You know r1 and r2, now solve for t.
{{{11t=55}}}
{{{t=5}}}
In 5 hours, they will be 55 miles apart.