An aircraft passes overhead at \(3 \mathrm{~km}\) altitude. The aircraft flies at \(M=1.5\). Assume the air temperature is constant at \(20^{\circ} \mathrm{C}\). Find the air speed of the aircraft. A headwind blows at \(30 \mathrm{~m} / \mathrm{s}\). How long after the aircraft passes directly overhead does its sound reach a point on the ground?