The per-unit power output of a salient-pole generator which is connected to an infinite bus, is given by the expression, $P=1.4 \sin \delta + 0.15 \sin 2 \delta$, where $\delta$ is the load angle. Newton-Raphson method is used to calculate the value of $\delta$ for $P=0.8 \: pu$. If the initial guess is $30^{\circ}$, then its value (in degree) at the end of the first iteration is
- $15^{\circ}$
- $28.28^{\circ}$
- $28.74^{\circ}$
- $31.20^{\circ}$