Answer
(a) increase
(b) $15.1^{\circ}$
Work Step by Step
(a) We know that if the frequency of light is decreased then the wavelength increases and therefore the angle of the first dark fringe increases.
(b) We know that
$\lambda=\frac{c}{f}$
$\lambda=\frac{3.0\times 10^8m/s}{5.22\times 10^{14}Hz}=57.5\times 10^{-9}m$
Now $\theta=\frac{m\lambda}{W}$
We plug in the known values to obtain:
$\theta=\frac{1\times 575\times 10^{-9}m}{2.20\times 10^{-6}m}$
$\theta=15.1^{\circ}$