3) A power cycle receives Q₁ by heat transfer from a hot reservoir atTH [ = 1200 K and rejects energy Qc by heat transfer to a cold reservoir at Tc = 400 K. For each of the following cases, determine whether the cycle operates reversibly, operates irreversibly, or is impossible. \text { a. } Q_{\mathrm{H}}=900 \mathrm{~kJ}, W_{\text {cycle }}=450 \mathrm{~kJ} \text { b. } Q_{\mathrm{H}}=900 \mathrm{~kJ}, Q_{\mathrm{C}}=300 \mathrm{~kJ} \text { c. } W_{\text {cycle }}=600 \mathrm{~kJ}, Q_{\mathrm{C}}=400 \mathrm{~kJ} \text { d. } \eta=75 \%