Answer: choice D) 18
Step-by-step explanation:
M is the midpoint of QR, so QM = MR, meaning that the two smaller pieces are equal (the two pieces combine back to QR)
Use substitution and isolate x
QM = MR
2x+5 = 5x-1
2x-5x = -1-5
-3x = -6
x = -6/(-3)
x = 2
If x = 2, then QM is
QM = 2x+5 = 2*2+5 = 9
and MR is
MR = 5x-1 = 5*2-1 = 9
both are 9 units long. Both are the same length as expected, so this helps confirm the answer.
The last thing we do is add up the two pieces QM and MR to get the length of QR. This is using the segment addition postulate.
QR = QM + MR
QR = 9 + 9
QR = 18
note: a negative length is never possible in any situation, so you can immediately eliminate choice B from the list of possible answers without even doing any math.