Answer
$\frac{d p}{d t}=8.0 \times 10^{-7} \mathrm{~N} .$
Work Step by Step
The sheet is perfectly absorbing, then the rate per unit area with which momentum is delivered to it is $I / c$, so
$$
\frac{d p}{d t}=\frac{I A}{c}=\\\frac{\left(119 \mathrm{~W} / \mathrm{m}^2\right)\left(2.0 \mathrm{~m}^2\right)}{2.998 \times 10^8 \mathrm{~m} / \mathrm{s}}\\=8.0 \times 10^{-7} \mathrm{~N} .
$$
