This problem comes from Car Talk.   An 18-wheeler truck driver has an unreliable fuel gauge.   His fuel tank is a cylinder that lies horizontally and is 20 inches in diameter.   He wants to know when his tank will be 1/4 full. He checks his fuel by putting a dip-stick vertically in his tank.
Solve for x in the diagram (when the fuel tank will be 1/4 full).

     




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