A leaves his school at the same time every day. If the travels at 18 km/h, he arrives home at 5∶30 p.m. If he travels at 8 km/h, he arrives home at 6∶15 p.m. At what speed (in km/h) must he travel to arrive home at 6∶00 p.m.?

• A. \(8\frac{2}{3}\)
• B. \(9\frac{1}{3}\)
• C. \(9\frac{7}{{11}}\)
• D. \(9\frac{9}{{11}}\)