How many MPG should l be getting roughly? and why does my AC and cold air smell damp and musty? checked the air filder and its clean :-s

37mpg combined as per Parkers.co.uk

This could vary with:

Driving style
Your use of A/C
Incorrect tyre pressures
Traffic intensity (stopping & starting always affects the MPG adversely)
and a few other factors.

As for the smell:

This is due to the build-up of mould and microbes on the evaporator. It can be cured with a microbiological treatment of the evaporator unit during the annual health check.