I think ans of APT shall be
calculate Return of factor 1 (Rf1) and then for factor 2 (Rf2) ans so on for all 5 factor using CAPM (i.e. calculate rm if other information is given )
and apply this
Er = rf + (Rf1-rf)beta of factor 1 + (Rf2 -rf) beta factor of 2 ans so on till 5
this will be return from APT