Answer:
2√10 km
Step-by-step explanation:
By Pythagoras theorem,
x^2 + 9^2 = 11^2
x^2 + 81 = 121
x^2 = 121 - 81
x^2 = 40
= 4 x 10
x^2 = 2^2 x 10
x = 2√10 km
