If QR is a median, then:
[tex]\dfrac{NO+MP}{2}=QR[/tex]
We have NO = 30, MP = 9x - 42 and QR = x + 15. Substitute:
[tex]\dfrac{30+9x-42}{2}=x+15\qquad\text{multiply both sides by 2}\\\\9x-12=2x+30\qquad\text{add 12 to both sides}\\\\9x=2x+42\qquad\text{subtract 2x from both sides}\\\\7x=42\qquad\text{divide both sides by 7}\\\\\boxed{x=6}[/tex]
Answer: A. 6
