depends on how much gear,gas people and prop size. Average amount of gear, full gas, 2 people 180-200 pounds and my old 40 hp merc 2 stroke trimed out (wot) about 27 mph @ 4800 rpm using a 12 pitch prop. The new 50 hp 4 stroke trimmed out (wot)about 26 mph @ 5800 rpm using a 12 pich prop.
The answer is in the "Miles per hour" (Mph) you drove. If you drove 40 Mph, then in one hour you would have driven 40 miles. Therefore, in five hours, at the constant speed of 40 Mph, you would have drive 200 miles.