Cambridge Secondary (7-9). Stage 8. MCE Science. Workbook - Unit 8: Forces and Motion - Question 9

Irfan enjoys horse riding. Early one morning, he rode a horse through the woods. The horse trots for 18 minutes and covers a distance of 4 km. It then speeds up to a canter and covers 7 km in 10 minutes. Irfan takes a 20-minute break to rest and enjoy the scenery. Finally, he sets off again and the horse gallops back home, covering 6 km in 6 minutes.

What formula do we use to calculate speed?