Find each momentum, then put them in order from smallest to largest.

Step 1. Ball $6\ \text{kg m/s}$; cyclist $225\ \text{kg m/s}$; trolley $10\ \text{kg m/s}$; stone $4.8\ \text{kg m/s}$.

Step 2. Order. Stone ($4.8\ \text{kg m/s}$), ball ($6\ \text{kg m/s}$), trolley ($10\ \text{kg m/s}$), cyclist ($225\ \text{kg m/s}$).