What is (4y-3)^3

(4y-3)^3   using a binomial expansion, we have

(4y)^3 - (3)(4y)^2*3 + (3)(4y)(-3)^2 - 27 =

64y^3 - 144y^2 + 108y - 27

What is y?? Can't figure it out if you don't give the variable.