b
(b)

\(N(\theta) \propto \frac{Z^2}{\sin ^4\left(\frac{\theta}{2}\right) E^2}\)

\(\text { or } N (\theta) \propto \frac{1}{\sin ^4\left(\frac{\theta}{2}\right)}\)

\(\theta=60^{\circ}\) and \(90^{\circ}\)

\(\therefore \frac{N(90)}{N(60)} \propto \frac{\sin ^4 30}{\sin ^4 45}\)

\(N\left(90^{\circ}\right)=x\)

\(N\left(60^{\circ}\right)=4 x\)