The speed of a boat downstream is 2.5 times its speed upstream. If the total time taken by the boat for going 15 km downstream and the same distance upstream is \(4\frac{2}{3}\) hours, then what is the speed (in km/h) of the boat downstream?
1
\(11\frac{1}{2}\)
2
\(11\frac{1}{4}\)
3
\(10\frac{5}{8}\)
4
10