**I have a question like that below,**

Suppose daily demand for gas is an exponential random variable with mean 5000 liters.Each day yhe tank is filled to full capacity.

a)What is the probability that the station sells more than 5000 litres?

b)Find the "median" daily salesin liters?

c)What size must the tank be to ensure that the probability of running out of fuel on any given day is %1?

I could not find a way to solve this problem.Please help me find a way.

Thanks;