Expectation of Continuous variable. Given the probability density function 
$$
f(x) =
\begin{cases}
\frac{cx}{3}, &  0 \leq x < 3, \\
c, & 3 \leq x \leq 4, \\
0 & \text{ otherwise}
\end{cases}
$$
I have found $c$ to be $0.4$ and $E(X)$ to be $2.6$. But I'm being asked to find $E(3X - 5)$ and I'm unsure of what to do.

$$\mathbf E(3\mathbf X-5)=3\mathbf E(\mathbf X)-5=3(2.4)-5=2.2$$
