$($b$)$ A $20-$kVA, $20000/480-$V$,60-Hz$ transformer has been tested to obtain the equivalent series impedance on the primary side. The short circuit test results on the primary side are as follows:

$P_{sc}=260W,V_{sc}=1130V,I_{sc}=1A$

Determine the approximate parameters of the transformer $R_{eq}$ and $x_{eq}.$ If the transformer is delivering a full load at rated voltage when the power factor is $0\mathrm{.}8$ lagging, determine the primary applied voltage $V_1$ and the transformer efficiency at full load when the core losses are $305$ W $.$