Question 56
To school by bicycle. Cátia leaves school every day at the same time and rides home by bicycle. When she pedals at $20~\mathrm{km}/\mathrm{h}$, she arrives home at $4:30$ in the afternoon. If she pedals at $10~\mathrm{km}/\mathrm{h}$, she arrives home at $5:15$ in the afternoon. At what speed should she pedal to arrive home at $17:00$?