An engine consists of a constant volume process at $0\mathrm{.}9$ m$3$ from $127$ kPa to $398$ kPa, an isothermal expansion until the pressure drops to its original value, and a constant pressure process returning to its original pressure and volume. Calculate the efficiency of this process if the gas is ideal and diatomic.

$[$Hints: $1.$ You need the volume at the end of the isothermal process. Find it easily with the ideal gas law! $2.$ For $|$QH$|,$ add the energy inputs during the constant volume and iosthermal processes.$]$