Read the information given below to answer these questions
a, b, c, d, e, f, g h and i are nine houses c is 2 km east of b a is 1 km north of b and h is 2 km south of a, g is 1 km west of h while d is 3 km east of g and f is 2 km north of g i is situated just in the middle of b and c while e just in middle of h and d.
Distance between a and f is _________.