Which one goes wit the answer

Measures of the angle of r, 31 s (x+4) t (3x+9)

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

Which statement best explains why ben uses the width hi to create the arc at j from point k