Answer:
15. x = 3
16. x = 3.5
Explanation:
As in the questions you have already answered, the base segment is twice the length of the midsegment.
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15. (x+9) = 2(2x)
9 = 3x . . . . . . . . subtract x
3 = x . . . . . . . . . divide by 3
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16. (10x -21) = 2(2x)
6x -21 = 0 . . . . . . . . subtract 4x
x = 21/6 = 7/2 . . . . . add 21, divide by 6
x = 3.5