Question 871368
start by finding the prime factors of 18 which are 3*3*2
we want to factor -x^2 + 7x + 18 
we have (-x +  ) times (x +  )
looking at the prime factors, we want to get a 7, note that 9 times 2 results in the 7, therefore
-x^2 + 7x + 18 = (-x + 9) times (x + 2)