I am stuck on the below question.

I have so far:

dq/dt = 48e^(-t)

1. The inflow to a small reservoir during a storm may be described by the equation, Q = 48.5 (1-e^(-kt))

Where Q = flow in m^(3)s^(-1)

k = runoff rate = 1.0 per hour

t = time in hours

The outflow through the dam gates is held constant at 40.5 m3s-1. The initial volume of the reservoir is 100 x 103 m3. Write down the differential equation describing the rate of change in reservoir volume with time.