Air is compressed steadily and adiabatically from $\backslash (20^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ and $96$ kPa to $\backslash (215^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ and $415$ kPa $.$ Assuming constant specific heats for air at room temperature, the isentropic efficiency of the compressor is $.$

$74\backslash \%$

$78\backslash \%$

$76\backslash \%$

$82\backslash \%$

$80\backslash \%$