Answer:
 11. HJ = 79; JK = 50
 12. HJ = 1; JK = 14
Step-by-step explanation:
The segment addition postulate tells you the total length is the sum of the segment lengths.
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11. HJ + JK + HK
 (6x -5) +(4x -6) = 129
 10x = 140 . . . . add 11
 x = 14 . . . . . . . divide by 10
 6x -5 = 6(14) -5 = 79 = HJ
 4x -6 = 4(14) -6 = 50 = JK
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12. HJ + JK = HK
 (4x -15) +(5x -6) = 15
 9x = 36 . . . . . add 21
 x = 4 . . . . . . . .divide by 9
 4(4) -15 = 1 = HJ
 5(4) -6 = 14 = JK