Suppose that you currently own a clothes dryer that costs $ 30 per month to operate . A new efficient dryer costs $670 and has an estimated operating...

Can someone please help me answer this question? I don't know how to do the calculations and I would appreciate any help very much. Thank you.

Suppose that you currently own a clothes dryer that costs $ 30 per month to operate . A new efficient dryer costs $670 and has an estimated operating cost of $ 20per month . How long will it take for the new dryer to pay for itself ?The clothes dryer will pay for itself in \\ months*