Hello! Please help me solve this step-by-step! Thank you

At the left end the cross section is a rectangle 1 foot by 2 feet perpendicular to the x-axis. At the right end the cross section is a rectangle 3 feet by 6 feet perpendicular to the xaxis, at x = 8 feet. Write an equation for dV, the volume of the rectangular slice shown, in terms of the sample points (x,y) in the xy-plane and (x,z) in the xz-plane. By suitable algebra, transform the equation in (a) so that (W is in terms of x alone. Find the volume of the tank. A cubic foot is approximately 7.5 gallons. How mayr gallons of fuel will the tank hold