Explanation

(c) ${\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ v}^{2} = u^{2} + 2as$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0 = \left( 50 \times \frac{5}{18} \right)^{2} + 2a \times 6$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ a = - 16\ {ms}^{- 2}\ \ \ \ \ \ \ \ (a = retardation)$
Again, $v^{2} = u^{2} + 2as$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0 = \left( 100 \times \frac{5}{18} \right)^{2} - 16 \times 2 \times s$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ s = \frac{(100\ \times 5)^{2}}{18 \times 18 \times 32} = 24.1 \approx 24\ m$