When an unpolarised light of intensity $I_0$ is incident on a polarising sheet, the intensity of the light which does not get transmitted is

In Young's double slit experiment, the slits are horizontal. The intensity at a point $P$ as shown in figure is $\frac{3}{4}{I}_0$ , where $I_0$ is the maximum intensity. Then the value of $\mathrm{\theta }$ is,
(Given the distance between the two slits $S_1 \mathrm{a}\mathrm{n}\mathrm{d} S_2 is 2\lambda$ )