Respuesta :

cottonsprout

Answer:

29 km

Step-by-step explanation:

to find the hypothenuse of a triangle you can use the pythagorean theorem.

a^2 + b^2 = c^2

in this case 20 km would be a, 21 km would be b and they add up to 841, then you find the square root and get 29 km :)