A walkway 63 m long moves at 0.8 m/s. A traveller walks along it at 1.0 m/s, the same way…

Step 1. $1.0\ \text{m/s} + 0.8\ \text{m/s} = 1.8\ \text{m/s}$.

Step 2. $t = \dfrac{63\ \text{m}}{1.8\ \text{m/s}} = 35\ \text{s}$.

Step 3. On plain ground: $\dfrac{63\ \text{m}}{1.0\ \text{m/s}} = 63\ \text{s}$. It saves $63\ \text{s} - 35\ \text{s} = 28\ \text{s}$.