foemula of density

If substance A has a density of ρA g/cm3 and substance B has a density of ρB g/cm3 . Derive an expression for the volume of B that would have the same mass as a volume of A (volA)

Let X be binomial with parameters n=15 and p=.2

(a) Find the expression for density for X

(b) Find the expression for the moment generating function for X

(c) Find E[X] and Var[X]

(d) Find P[X <=1] by evaluating the density directly.