For an isobaric process, the first law gives: Q=ΔU+W.
For a diatomic gas with γ=1.4, we have CV=25R and CP=27R.
Since W=nRΔT=100 J for isobaric expansion, the change in internal energy is: ΔU=nCVΔT=25nRΔT=25×100=250 J.
Therefore, Q=250+100=350 J.