Can u plz help me with this 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

Note jointly means multiplied inversely in devide

Answer 1

[Recall: The phrase "u varies directly as v" means u = kv, for some real number k.]

y = k (x³ z²) / (x + z)²

72 = k(8*9) / 25
[72(25)] / 72 = k
k = 25

y = (25) [(-25) / 16]
= - 625 / 16 = -39.0625