Eight more than a number z is less than or equal to 10

I'm terrible at math any here is appreciated.

Determine the mean and variance of the random variable with the following probability mass function. f(x)=( 729divided by 91) (1 divided by 9) superscript x baseline comma x equals 1,2,3 round your answers to three decimal places (e.g. 98.765).

For f(x)=2x+3 and g(x)=x^2- 8 find (f+g) (x)