Thunder and lightning: how far away?

During a storm you count the seconds between each flash and its thunder. You will make the program turn each count into a distance, find the nearest strike, and count how many strikes were closer than $1\ \text{km}$. Then it draws the distances as bars.

The idea. The light arrives almost at once, so the counted time is the sound's travel time: $d = vt$ with $v = 340\ \text{m/s}$.

Your tasks.

1. Inside the loop, work out d, the distance of each strike, in metres.
2. Find nearest, the distance of the nearest strike, in metres.
3. Find close, how many strikes were less than $1000\ \text{m}$ away.