A $150-$kVA, $2400/240-$V transformer has the following parameters referred to the primary side: Re$1$

$=0\mathrm{.}5$ and Xe$1=1\mathrm{.}5.$ The shunt magnetizing impedance is very large and can be neglected. At

full load, the transformer delivers rated kVA at $0\mathrm{.}85$ lagging power factor and the secondary voltage

is $240$ V$.$ Calculate:

a$)$ The voltage regulation

b$)$ The efficiency assuming core losses amount to $600$ W$.$