The cost of fuel to propel a boat through the water (in dollars per hour) is proportional to the cube of the speed v. a certain ferry boat uses $100 worth of fuel per hour when cruising at 10 miles per hour. apart from fuel, the cost of running this ferry (labor, maintenance, and so on) is $3125 per hour. (a) find the proportionality constant for the cost of the fuel per hour. do not round your answer.