_Here is the step by step solution:_
1. Durango, Mexico is located at (24.0333° N, 104.6667° W)
2. Leon, Guanajuato, Mexico is located at (21.1231° N, 101.6667° W)
3. The distance between Durango and Leon is
$$d=\sqrt{(x_{Leon}-x_{Durango})^2+(y_{Leon}-y_{Durango})^2}$$
$$d=\sqrt{(101.6667-104.6667)^2+(21.1231-24.0333)^2}$$
$$d=\sqrt{(-2)^2+(-2.9102)^2}$$
$$d=\sqrt{4+8.4692}$$
$$d=\sqrt{12.4692}$$
$$d=3.528 \ km$$