A totally reflecting small plane mirror placed horizontally faces a parallel beam of light as shown in the figure. The mass of the mirror is $200 \mathrm{g}$. Assume that there is no absorption in the lens and that $20\%$ of the light emitted by the source goes through the lens. The power of the source needs to support the weight of the mirror is $P \times {10}^8 \mathrm{watt}$, where $P$ is [take $g = 10 \mathrm{m} {\mathrm{s}}^{-2}$]