# Wait a minute!

On a nice sunny day, John saw a supersonic fighter plane flying parallel to the ground. As a student of Aeronautical Engineering, he knew off-hand the speed of the plane was 1.25 Mach. He could hear its sonic boom, 12 seconds after the plane flew directly overhead. What is the altitude of the plane in km?

• Assume speed of sound in air to be $$330 \text{ m/s}$$.
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