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**daskywalker** Three spheres, A, B and C, each 1 inch in diameter, are arranged on a horizontal flat surface so that they touch each other and their centers form an equilateral triangle. A fourth sphere D, also 1 inch in diameter, is placed on top of the other three so as to form a regular tetrahedral configuration (it touches each of the other three spheres).

(a) What is the distance between the centers of the spheres?

(b) How far above the flat surface is the center of sphere A?

(c) How far (vertical distance) above the center of sphere A is the center of sphere D?