Need help breaking down this question. I don't understand the formulas at all.

Let X be a random variable with the following probability distribution. Value x of X P(X=x) 3 0.25 4 0.15 5 0.15 6 0.45 Complete the following. (If necessary, consult a list of formulas.) (a) Find the expectation E (X) of X. E(X) = 1 (b) Find the variance Var(X) of X. var (X) = 0