From the given transfer characteristic of a transistor in CE...

The formula to calculate the current gain $\left(\beta\right)$ in CE configuration is given by

$\beta = \dfrac{∆ {I}_{C}}{∆ {I}_{B}} . . . \left(1\right)$

Considering the third and the first points on the given graph, the current gain can be calculated as follows:

$\begin{cases}\beta & = & \dfrac{\left(30 - 10\right) \times {10}^{- 3}A}{\left(300 - 100\right) \times {10}^{- 6}A} \\ & = & 100\end{cases}$

The formula to calculate the power gain \left(P\right)$in CE mode can be written as</p><p>$P = {\beta}^{2} \cdot \dfrac{{R}_{C}}{{R}_{B}} . . . \left(2\right)$</p><p>Substitute the known values of the parameters into equation (2) and solve to calculate the required unknown parameter.</p><p>$\begin{cases}{10}^{x} & = & {100}^{2} \times \dfrac{1kΩ}{10kΩ} \\ & = & 1000 \\ & = & {10}^{3} \\ & ⇒ & x = 3\end{cases}