Astraight rod consists of a 1.2-cm-long piece of aluminum attached to a 2.0-cm-long piece of steel. part a by how much will the length of this rod change if its temperature is increased from 20∘c to 40∘c?

Okay now the answer Mastering accepted was 0.0010 cm, if you actually calculate it which is the same as your 1.0 E^-5 except that answer was in m not centimeters, so you multiply it by 100cm/m.

You might want to check to make sure you used the right alpha levels (23 E^-6 for aluminum and 12 E^-6 for steel)

Hope this helps!