A `30.0 cm` long metal rod expands by `0.0650 cm` when its temperature is raised from `0^(@)C` to `100^(@)C`. A second rod of different metal and of the same length expands by `0.0350 cm` for the same rise in temperature. A third composite rod, also `30.0 cm` long, is made up of pieces of each of the above metals placed end to end and expands by `0.0580 cm` when temperature is increased from `0^(@)C` to `100^(@)C`. the length of the longer portion of the composite bar in cm at `0^(@)C` is