Physics question

Myron is supported by a stationary hot air balloon directly above John who fires a pistol at the balloon. It is not clear to John whether his bullet strikes the balloon on the way up or on the way down, but the time between the pistol firing and the balloon bursting is the same as the time between the balloon busting and John hearing the bursting of the balloon. The initial speed of the bullet was about 1% greater than the speed of sound (344m/s). 


Question: How high was the balloon when it burst? Ignore air resistance. Please provide full solution.