A Brayton gas turbine cycle has two stages of compression and two stages of expansion. The pressure ratio across each stage of the compressor and turbine is 3. The air enters each stage of the compressor at 300K and each stage of the turbine at 1200K. If the efficiency of each compressor is 80% and each turbine is 85% Determine: using variable specific heat method for: Case 1) no regenerator a) The back work ratio b) The thermal efficiency