Answer:
C. -2n+3/n-4
Step-by-step explanation:
(n^2+10n+21)/(n^2+3n-28)-(3n/n-4)
(n^2+7n+3n+21)/(n^2+7n-4n-28)-(3n/(n-4)
(n(n+7)+3(n+7))/(n(n+7)-4(n+7))-(3n/n-4)
((n+7)(n+3)/(n+7)(n-4))-(3n/n-4)
(n+3/n-4)-(3n/n-4)
n+3-3n/n-4
-2n+3/n-4
