A town has a circular boundary which has four gates. A soldier starts walking from the North gate towards North. At the same time another soldier starts walking from the East gate towards East. What is the minimum distance traveled by both soldiers together till the point when they can just see other, if radius of the circular boundary is 10 km?

a)14.6 km
b)12.5 km
c)7.3 km
d)8.2 km