Explanation

(b) The given equations of waves be written as
$y_{1} = 0.25\sin(310t)\ \ \ \ \ \ \ \ \ \ \ \ \ \ldots(i)$
And $y_{2} = 0.25\sin(316t)\ \ \ \ldots(ii)$
Comparing Eqs. (i) and (ii) with the standard wave equation, written as
$y = a\sin(\omega t)\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ldots(iii)$
We have, $\omega_{1} = 310$
$\Longrightarrow v_{1} = \frac{310}{2\pi}unit$
And $\omega_{2} = 316$
$\Longrightarrow v_{2} = \frac{316}{2\pi}unit$
Hence, beat frequency=$v_{2} - v_{1}$
$= \frac{316}{2\pi} - \frac{310}{2\pi} = 3\pi\ unit$