Expectation of Continuous variable. Given the probability density function 

$$
f(x) =
\begin{cases}
\frac{cx}{3}, &amp;  0 \leq x &lt; 3, \\
c, &amp; 3 \leq x \leq 4, \\
0 &amp; \text{ otherwise}
\end{cases}
$$

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