At 10, A went eastward by 2 times 6, which was equal to 12 km.

B Go north at 10. 1 times 5 equals 5 kilometers.

Using Pythagorean Theorem

Because due east and due west are right angles

So the square of the distance is 12 plus the square of 5, and then the square is 13.

Therefore, the distance is 13km.

And because 13 is less than 15.

So you can keep in touch.