A Metallic Sheet Has a Large Number of Parallel Slits $5.0 \mathrm {~mm}$

A metallic sheet has a large number of parallel slits, $5.0 \mathrm {~mm}$ wide and $20 \mathrm {~cm}$ apart. This sheet is used as a diffraction grating for microwaves. A wide parallel beam of microwaves is incident normally on the sheet. If the intensity maxima occur $2.0 ^ { \circ }$ apart in the central region, what is the wavelength of the microwaves?

A) $8.0 \mathrm {~mm}$
B) $9.0 \mathrm {~mm}$
C) $7.0 \mathrm {~mm}$
D) $5.0 \mathrm {~mm}$
E) $6.0 \mathrm {~mm}$