Can u Plz help me with a precalc problem?

Question

y varies jointly with the cube of x and the square of z and inversely with the square of the sum of x and z if y = 72 when x= 2 and z=3 , then find the value of y when x= -1 and z=5.....thx...... I am very lost plz explain all work and answers in detail thx

Answer 1

There must be a proportionality constant; call it k. Then we have y = k x^3 z"2 /(x+z)^2. If y = 72 when ..., we can evaluate k: 72 = k 2*3 3^2 /(2 + 3)^2, so k = 72(25)/72, or 25. The rest is obvious.

Answer 2

Just a quick guess off the top of my head would be that the problem would be set up like this y-(x+z)^2=(x^3)*(y^2)-(x+z)^2

That would make y = -25