My teach said there was a common factor to factor out before i can substitute the value of 1 in for x, but i have no clue how to find it..

(3-x)/(3x^2-9x)

if i put zero in on the bottom it becomes 0 and i can't divide by zero, someone please show me their solutions, don't skip any steps please (and if u could, explain some of the steps that would be great)