(d) For a transistor amplifier in common emitter configuration, current gain
$A_{i} = \frac{h_{fe}}{1 + h_{oe}R_{L}}$
where $h_{fe}\ $and $h_{oe}\ are\ hybrid\ parameters$ of a transistor.
$\therefore\ A_{i} = \frac{50}{1 + 25 \times 10^{- 6} \times 1 \times 10^{3}} = - 48.78$