Maybe some of the answers to this question from ~3 years ago might help you

https://www.researchgate.net/post/How_to_derive_the_formula_for_calculating_expectation_of_a_discrete_random_variable_using_CDF

Good luck

For a discrete random variable, the expected value, usually denoted as E(X), is calculated by multiply each value x, in the support by its respective probability f(x), and then add them all together.

The variance of a discrete random variable is calculated as: take each value of x, subtract the expected value, square that value and multiply that value by its probability. Then sum all of those values.

E(X)=SUM(f(X)*X) and Var(X)=SUM[(X - E(x))^2*f(X)]. But ..., why not use wikipedia as the pages are more than decent. After it, apply your new knowledge and check the results? https://en.wikipedia.org/wiki/Variance