(a) The given equation is
$y = 5\sin\frac{\pi}{2}(100t - x)$ …(i)
Comparing Eq. (i) with standard wave equation, given by
$y = A\sin{(\omega t - kx)}$ …(ii)
we have
$\omega = \frac{100\pi}{2} = 50\pi$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \frac{2\pi}{T} = 50\ \pi$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ T = \frac{2\pi}{50\pi}$ =0.04 s