The magnetic flux linked with coil, in weber, is given by the equation, $\varphi =5t^2+3t+16$ The induced emf in the coil in the fourth second is

$\left|\mathrm{e}\right|=\frac{\mathrm{d\varphi }}{\mathrm{dt}}=\frac{\mathrm{d}}{\mathrm{dt}}\left(5{\mathrm{t}}^2+3\mathrm{t}+16\right)=(10\mathrm{t}+3)$

$\begin{array}{r}\text{ When }t=3\mathrm{s},\left|e_3\right|=(10\times 3+3)=33\mathrm{V}\\ \text{ When }t=4\mathrm{s},\left|e_4\right|=(10\times 4+3)=43\mathrm{V}\end{array}$

Hence, emf induced in fourth second

$=\left|e_4\right|-\left|e_3\right|=43-33=10V$