Help did i do thing completely wrong??

hi, in paper 1 question 14 part c i did it completely different to everyone else most people used the values 180 and 0 and subbed them in but I did it like this: if you multiply the factors of a line you get the equation we can get the factors by getting the roots and we know the roots of this are 3 because it told us the graph was symmetrical. So therefore the factors are x-3 and x-3 I just multiplied these out and it matched the function given just with numbers instead of letters. I don't know a single person who did it this way but!! I started doing it the same way as everyone else but my numbers seemed weird and I thought because the bothered to say that the graph was symmetrical that they wanted it done this way. I got 9 out for C not 180 but i feel that it could be something to do with multiples which I know you cover in the leaving cert course. Is this right and if not will i get some marks for it? Thanks!!

JackW— 30/06/16