I'm also stumped by this one:

Question

3. A bimetallic strip (117 cm by 1 cm by 0.01cm) has aluminum (a = 23x10^-6 1/Celsius) on one side and has steel (a= 12x10^-6 1/Celsius) on the other. It is perfectly straight at room temperature (20 celsius). What change in temperature is required to change the strip into a full circle? (assume change in thickness is negligible)

"a" is the coefficient of linear thermal expansion and can be defined as the fractional change in length of a specific substance that has undergone a change in temp. of 1 degree Celsius.

Again, any starting points are appreciated!