Calculating Linear Expansion of Iron Rod for 2.51cm Ring Diameter

[furielrage]

An iron rod has a diameter of 2.50cm at 20.0°. To what temperature must it be heated to fit into a ring with an inside diameter of 2.51cm. I'm given: alpha=1.0x10^-5

I'm not sure how to apply it to the △L=(alpha)(object length)△T

 

[Psi-String]

Since the diameter is one dimensional quantity, L=2.50cm.
It seems a little bit strange but the diameter will expand just like a iron rod.