\(3 \frac{3}{5} + \frac{3}{20} = 3 \frac{12}{20} + \frac{3}{20} = 3 \frac{15}{20} = 3 \frac{3}{4}\) км
\(3 \frac{3}{5} - \frac{17}{20} = 3 \frac{12}{20} - \frac{17}{20} = 2 \frac{32}{20} - \frac{17}{20} = 2 \frac{15}{20} = 2 \frac{3}{4}\) км
\(3 \frac{3}{4} + 3 \frac{3}{4} + 2 \frac{3}{4} = 9 \frac{9}{4} = 11 \frac{1}{4}\) км
Ответ: \(11 \frac{1}{4}\) км.