Temperature Required for Brass Plug and Iron Ring to Fit

Jayhawk1 said:

A brass plug is to be placed in a ring made of iron. At room temperature (20oC), the diameter of the plug is 8.755 cm and that of the inside of the ring is 8.745 cm. They must be brought to what common temperature (in Co) in order to fit? The coefficient of linear expansion for brass is 10x10-6(Co)-1 and that for iron is 12x10-6(Co)-1.

I don't know what to do with this... I know I have to subtract and divide some of these numbers, but I have no clue as to how to do it exactly. I need help please! Thank you.,