DX=EX^2-(EX)^2=3

E(X^2)=DX+(EX)^2=3+ 1=4

e[3(x^2-2)]=3[e(x^2)-2]=3(4-2)=6

This is the nature of expectation and variance.

E(aX+b)=aE(X)+b

D(aX+b)=a^2D(X)

So a is correct.