This is the boss. No calculator — the numbers are chosen to fit in your head, the way boss numbers should be. One delivery route, and every answer feeds the next: each leg's time from its speed, then the whole trip's distance–time slope, then the litres the van drinks for it. Write each line down as you go — one early slip rides along to the end of the route.

Everything in this chapter was secretly about rates. Prove it. 5★ under par here is the chapter crown. Buckle up.