Maths statistics, expectation and variance question im stuck on

stuck on this question:
the probability distribution of the discrete random variable x is given by
p(x=r) = 2r-1/16 for r = 1 2 3 4
p(x=r) = 0 otherwise.

i) find E(X), which i got 3.125
but stuck on part 2
ii) find P(X<μ)

will -

Perfect! E(x) = 3.125

Now, μ = E(x) = 3.125

P(X < 3.125) = P(1) + P(2) + P(3)

= 0.0625 + 0.1875 + 0.3125 = 0.5625

Hope that helps