Thank you. I've just realised that i've had the sizing wrong which was way i've kept getting wrong answers...(Original post by elekro)
so the walls alone(without ceiling and floor, as the problem states that Stephanie wants to paint just the walls) are 80m^2 (because two walls are 9.2x2.5 and the others are 6.8x2.5). So for one coat of paint you need 4 tins, thus for two coats you need 8 tins, which will cost you 94 pounds.
Find out how.