Three friends divided some bullets equally. After all of them shot 4 bullets the total number of bullets remaining is equal to the bullets each had after division. Find the original number divided.
Starting with 3X bullets, each gets X and has (X - 4) left after the shooting. Solve 3(X-4) = X gives X = 6 and so we end up with 3X = 18 as Aquagility rightly says.