Tennis balls cost $7 for one can of three balls. DJ gives the cashier $40 to buy balls and receives $12 back in change. How many tennis balls did DJ buy?

Find the volume of the described solid.the solid lies between planes perpendicular to the x-axis at x = 0 and x=7. the cross sectionsperpendicular to the x-axis between these planes are squares whose bases run from the parabolay=-31x to the parabola y = 30/x.a) 441b) 147c) 864d) 882