Answer
See answer below.
Work Step by Step
An ideal process in the three cases is a reversible and adiabatic (isentropic) process.
a) $\eta = \frac{\mbox{actual output}}{\mbox{isentropic output}}$
b) $\eta = \frac{\mbox{isentropic input}}{\mbox{actual input}}$
c) $\eta = \frac{\mbox{actual outlet's k.e.}}{\mbox{isentropic outlet's k.e.}}$
