need help with stochastic question

Customers arrive at a single server station as a Poisson process With rate A = 1/3. The service times Y1, Y2, are i.i.d. with distribution as sum of two uniform random variables in (07 1), that is each K- has distribution the same as Ui + W, Where U1, W are two independent random variables with uniform distribution on (0, 1). Calculate in the equilibrium, What is the mean queue length L (including the customer at the server)