Question 22
Antonio walked $11.5\text{ km}$ to his cousin Maria’s house. At first he walked uphill, then along a flat part of the road and the final part was downhill. The trip took 2 hours 54 minutes. The next day his walk back home took 3 hours 6 minutes. Antonio walks uphill at a constant speed of $3\text{ km/h}$, on the flat at $4\text{ km/h}$ and downhill at $5\text{ km/h}$. What is the length, in kilometres, of the flat part of the road?