This is the concept of applications of volume. We are required to calculate BTUs per cubic foot. This will be given by the formula: (BTU)/volume Total BTU=15*750=11,250 (assuming the bus is a perfect cuboid) volume of the bus will be; volume=length*width*height =38*8.5*6.25 =2018.75 ft^2 Thus the BTUs per foot will be: 11250/2018.75 5.57 BTUs/ft