Help me im so bad at this

What number must you add to complete the square x^2+12x=16

One integer is 8 times another. if the product is 72, then find the integers

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