I need help with some math problems

first problem: w varies jointly as P and Q, and inversely as the square of T. If W= 54 when P=45 Q= 6 and T= 6, find W if P=25,Q=20 and T=30.

Second problem: a variable A varies inversely as the square of b. If A is 5/9 when b is 3, find A when b is 9.

third problem: A variable P varies jointly with M and the square of n. If k is the constant of proportionality, find the equation of the variation.

w = k (PQ/T^2) --> k = 36/5

w = (36/5)(25)(20)/(30)^2 = 4