I need help

I Suppose you go to a store where there are two cashiers, one of whom is efficient and the time they need to take care of a customer has an exponential distribution with mean 1 (minute). The other is new to the job and the time they need to take care of a customer has an exponential distribution with mean 3. Find the distribution of time you will spend being served if you are randomly assigned by the toss of a coin to a cashier. Also determine the survival function, hazard rate and mean and variance of the distribution of time you will spend being served