So in this question I am told that a supermarket claims that the mean time to serve a customer is equal to 4 mins.However, a customer claims it is greater than 4 mins. I am asked based off a sample of n=9, determine the form of the best test of which has size of a=0.05

So I know my Ho: λ=4 and my Ha: λ>4

I am just unsure on how to derive it down, I know I use the central limit theorem like in previous examples I have done but very unsure for exponential distribution !