Using \displaystyle {{v}^{\ 2}}={{u}^{\ 2}}+2as \ \ gives
\displaystyle \begin{align} & {{15}^{2}}={{5}^{2}}+2\times a\times 500 \\ & 200=1000a \\ & a=0\textrm{.}2 \text{ m}{{\text{s}}^{\text{-2}}}\\ & \\ \end{align}
