Let $X$ have the probability density function $f(x;a) = \frac{1}{a}e^{-x/a}, 0 < x < \infty$; $\Omega = \{a; a = 2,4\}$
To test the simple hypothesis $H_0: a = 2$ against the alternative simple hypotheses $H_1: a = 4$, a random sample of $X_1,X_2$ of size $n = 2$ will be used. Define the critical region to be $C = \{ (x_1,x_2): 9.5 <= x_1 + x_2 < \infty\}$. Calculate:
i) the significance level of the test, and ii) the power of the test.
So to calculate the significance level i said $P(9.5 <= x_1 + x_2 < \infty |H_0 \text{ is true})$ but i'm not sure how to proceed from there and for ii) I have no clue.