The

co-ordinates have to be the same in order for something to be due south of something.
Thus, we have to see, how long it takes for the

co-ordinates to become equal.
Thus, we got that the speed is

So, the

co-ordinate of A is

.
Thus,

The total time to get to the point
)
is 7 seconds,

.
Thus you simply add the new value to

. And you get the answer:
