(n^2+9n+14)/(7n+14)=3n-n    | *( 7n+14)

n^2+9n+14=21n+42-7n^2-14n

8n^2+2n-28=0    | /2

4n^2+n-14=0

D=1+224=225

n1=(-1+15)/8    n1=1.75

n2=(-1-15)/8    n2=-2