A child on a sled has a horizontal velocity ($v$) of $6.0\text{ m/s}$ after going down a snowy hill when the child and sled combination encounters a smaller hill. It is assumed that:

- The child and the sled have a total mass of $45\text{ kg}$.
- Friction and air resistance are negligible.
- The child and sled coast to a complete stop at the top of the smaller hill.

Which of the following most closely approximates the height of the smaller hill?