Question 324687
Factoring a trinomial is the opposite of the FOIL method.  The binomial factors will have this form:
(s   A)(s   B)
where A and B will be the factors of the third term (18). The factors of 18 are: 1, 2, 3, 6 , 9 and 18. So these are our possibilities of A and B: 1&18, 2&9, 3&6.
Now, we need to see what combination, when added, will equal -9 (since the second term is -9s.
We know that both numbers must be negative because when added they equal a negative number, but when multiplied, they equal a positive number.  The only possibility is -6 and -3.
So your answer is:
(s-3)(s-6)