That kind of depends on where the ship is now, and where it wants to go.
We learn these kinds of things in navigation school, and I'll just bet that
it's the kind of information that's right there in the part of the question
that you didn't bother copying.
Explanation:
what are the other words ?
Answer:
1 hour
Explanation:
Since the definition of velocity is
, we can calculate the position at time t of an object moving at speed v with
.
The position of the first ferry is 
The position of the second ferry is 
We want to know when they will be 6 miles apart. This means, if we call that distance d, that we want to know when the difference between their positions will be d, or
(we know that at the beginning the position of the ferry 1 is of higher value than that of ferry 2 since it left before).
We use our previous formulas then:

Since we want the time, we do:

And substitute our values:
