Explanation:
x = distance event to point A in ft
y = distance event to point B in ft = x + 2×1100
the distance is 2 seconds the speed of sound longer than x.
AB = 4 miles = 21120 ft (5280 ft in 1 mile)
so, we have a Pythagoras right-angled triangle situation :
c² = a² + b²
with c being the Hypotenuse (side opposite of the 90° angle), which is y in our case, as the right angle is at point A (the event is due north of A).
so, we have
y² = x² + 21120²
(x + 2200)² = x² + 21120²
x² + 4400x + 4,840,000 = x² + 446,054,400
4400x = 441,214,400
x = 100,276 ft = 18.99166667... miles
the fireworks display is 100,276 ft north of point A.
which is very far. I don't think they would see or hear anything.
so, I hope the information in the question is typed correctly. there are clearly some mistakes regarding point A and B. but I thought I could correct this logically.