As Diesel guestimated the distance to the horizon, so I guestimated the angle A to 60deg
That gives a ratio of the triangle side as 3:4:5
Therefore, 3.24:C/2:the other one.....
Formula (3.24/3)*4 = C/2 or C = 8*1.08 = 8.64
As we are guessing a bit, lets call it 10 miles, or 16 Ks