For this problem we are going to use a 400 gallons tank. You can apply the same procedures to a bigger or smaller tank.
The first thing we are going to do id divide the horsepower of the engine (342) by the rate of gallon consumption (
18) to find how many gallons our engine will consume in one hour:
gallons per hour.
Next, we are going to divide the half tank of fuel by our engine consumption per hour:
Since the full tank is 400 gallons, half tank will be 200 gallons.
hours
We can conclude that the boat will run for 10.5 hours at 342 horsepower on a half tank of fuel.