From Mechanics

We use the results of the first two parts of the question.

As the sprinter runs \displaystyle \text{16 m} in the first stage of the race he must run \displaystyle \text{84 m} in the second stage.

For the second stage we use \displaystyle s=ut+\frac{1}{2}a{{t}^{\ 2}} with \displaystyle a=0 giving

\displaystyle \begin{align} & 84=8t+0 \\ & t=10\textrm{.}5\ \text{s} \\ \end{align}

The total time taken is \displaystyle 14\textrm{.}5\ \text{s}