Move the six to the other side to yield:
[tex]n^{2} + 3n - 18 = 0[/tex]
Split up the middle term into factors of -18.
[tex]n^{2} - 3n + 6n - 18 = 0[/tex]
Factorise.
[tex]n(n - 3) + 6(n - 3) = 0[/tex]
Group like terms.
[tex](n + 6)(n - 3) = 0[/tex]
Thus, n = -6 and 3
