Cycling and walking time model

Optional extension

A cyclist rides \(40\) km at \(x\) km/h before a breakdown, then walks \(8\) km at \((x-16)\) km/h. The whole trip takes \(4\) hours.

1. Write the cycling time.[2]
2. Write the walking time.[2]
3. Form an equation and show that \(x^2-28x+160=0\).[2]
4. Solve and reject the invalid root.[2]
5. Find, in hours and minutes, the time for all \(48\) km if completed at the original cycling speed.[2]