Power of a most powerful test with a stated size

Let $X$ be an observation from a population with density function $f(x)$. Then the power of the most powerful test of size $\alpha=0.19$ for testing

$$H_0:f(x)=\begin{cases}\frac x2, & 0<x<2,\ 0, & \text{otherwise,}\end{cases}\quad\text{against}\quad H_1:f(x)=\begin{cases}\frac{3x^2}8, & 0<x<2,\ 0, & \text{otherwise,}\end{cases}$$

is equal to ____________