Ruler-drop reaction times

Deepa does the ruler-drop test six times. Her first try is a warm-up. You will turn each catch into a reaction time, find her average after the warm-up, and draw her tries as a bar chart.

The idea. A ruler that falls $d$ metres takes $t = \sqrt{\dfrac{2d}{g}}$ seconds, with $g = 9.8\ \text{m/s}^2$. The catches are in centimetres, so divide by $100$ first.

Your tasks.

1. In reaction_ms, return the reaction time in milliseconds for a catch of d_cm centimetres.
2. Set times to the list of reaction times, one for each catch, in the same order.
3. Set average_ms to the average of the last five times.