The brain can sense the direction of a sound source by noting how much earlier a sound is heard in one ear than in the other. Model your ears as two sensors 19.0 cm apart. If a click from a distant source is heard 210 x 10^-6 s earlier in the left ear than in the right, from what direction does it appear to originate? I've tried a bunch of methods to get a few desired values, but I tend to have an additional unknown variable or I end up canceling the desired value in the process to end up with something near 1 = 1. The problem seems to be more mathematical than physical. The answer I'm supposed to receive is 22.3 degrees left of center.