A racing track needs bends. We build it from stretches: add(60, 2) is 60 segments bending right by 2. Straights have
0, left bends are negative. It is still 800 segments in all.
Each add puts count segments with the same curve at the end of the list, so the calls are the track from start
to finish: a straight, a gentle right, a straight, a left...
80 + 60 + 50 + ... + 90 is 800 segments.
Your turn
In buildTrack, replace add(800, 0) with these thirteen lines. The trackLength line stays.