Answer:
CD = 3
Explanation:
Triangles CBA and CDE are similar (AA), so the side lengths are proportional.
(15-x)/20 = x/5
Multiplying by 20 gives ...
15 -x = 4x
15 = 5x . . . . . . add x
3 = x . . . . . . . . divide by 5
CD = x = 3
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