How can i write a proportion using a 3-d model like this

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

:24% of students in a class are girls. if there are less than 30 students in this class, how many students are there? how many girls are there?

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)