Timing nerve messages

A message from the skin travels along a nerve to the spinal cord. You will write a function that gives the time for an impulse, use it for three nerves, and find the slowest message.

The idea. Time is the length divided by the speed. Multiply by $1000$ to change seconds into milliseconds.

Your tasks.

1. In impulse_ms, return the time in milliseconds for an impulse to travel length metres at speed m/s.
2. Fill the dictionary times with the time for every nerve in nerves.
3. Set slowest to the name of the nerve whose message takes the longest.