Applied Decision Methods, Business, Expected value and variance formulas in excel

I need an excel spreedsheet for this problem.....should take a couple of minutes if you know what youre doing

Cars arrive at Carla's Muffler shop for repair work at an average of 3 per hour, following an exponential distribution.

(a) What is the expected time between arrivals?  ( use the Expected Value formula in excel)

(b) What is the variance of the time between arrivals? ( Variance formula excel)