How Do You Calculate Thermal Efficiency in a Diatomic Gas Heat Engine Cycle?

[Eagle's Wings]

Homework Statement

You build a heat engine that takes 1.00 mol of an ideal diatomic gas through the cycle abc, where segment bc is isobaric and segment ca is isochoric. calculate the thermal efficiency of the engine.

this is a 5 part problem and I already solved for Wo and Wo=Qo I solved for Ta, Tb, and Tc. Ta=Tb. the problem gives me Va, Vb, Pa, and Pb in the figure.

Homework Equations

e = W/Q$_{H}$ = 1 - |Q$_{C}$/Q$_{H}$|

W = |Q$_{H}$| - |Q$_{C}$|

The Attempt at a Solution

I know that there are other ways to solve for e, but I don't know how to solve for e in this problem. I am completely lost. I can't use Carnot because that's for an ideal system, I can't use the one for the otto cycle because i don't have r and the problem doesn't tell me that it is otto cycle problem. WHAT DO I DO?

 

[Eagle's Wings]

also the segment ab is isothermic. I don't see how that would help any though

 

[Eagle's Wings]

just kidding, i just figured it out. i can use the equation of heat entering the system which is Qh which is on segment bc which is isobaric so i can use Cp to solve for Qh!