(d) The equation is given
$y = 5\sin{\pi(t + 4)}$ …(i)
The standard equation is
$y = A\sin{(\omega t + \varnothing)}$ …(ii)
Now comparing Eqs. (i) and (ii), we get
$A = 5\ m,\ \ \omega t = \pi t\ \ \ \ \ or\ \ \ \omega = \pi$
So, $T = \frac{2\pi}{\omega} = \frac{2\pi}{\pi} = 2$ s