Answer
$6.38W/cm^2$.
Work Step by Step
The first polarizer filters out half the incident unpolarized light.
$$I_1=\frac{1}{2}I_o$$
The fraction filtered out by the second polarizer depends on the angle between the axes of the two polarizers. At the end:
$$I_2=I_1cos^2\phi=\frac{1}{2}I_o cos^2 \phi $$
$$I_2= \frac{1}{2}(20.0W/cm^2) cos^2 37^{\circ} $$
$$I_2= 6.38W/cm^2$$
