So, the problem is:

X is a random variable with E(x) = 100 and V(x) = 15. Find:

a) E(x^2)

b) E(3x+10)

c) E(-x)

d) V(-x)

e) std dev(-x)

For part a), i used the equation that V(x) = E(x^2) - (E(x))^2, so 15 = E(x^2) - 10000, therefore E(x^2) = 10015

I'm not sure at all where to start with b, any pointers?

for c, E(-x) would equal -100, right? I think this is assuming that the pmf still exists for x having negative values, and that the probabilities are the same...is this correct?

using the same equation as part a, i found V(-x) to equal 15 as well, since squaring a negative number still results in a positive one, and so the std. dev of (-x) would be sqrt(15)?

Thanks!