A train moving at 54 km/h slows at a steady 0.3 m/s² as it comes into a station…

Step 1. Units. $u = 15\ \text{m/s}$, $v = 0$, $a = -0.3\ \text{m/s}^2$.

Step 2. (a) $0 = 15\ \text{m/s} - 0.3\ \text{m/s}^2 \times t$, so $t = 50\ \text{s}$.

Step 3. (b) $0 = (15\ \text{m/s})^2 - 2 \times 0.3\ \text{m/s}^2 \times s$, so $s = \dfrac{225\ \text{m}^2/\text{s}^2}{0.6\ \text{m/s}^2} = 375\ \text{m}$.