Review how to do polynomial long division and give it a try. You will find that you need a value of c such that
(c+3) x -12 is evenly divisible by x-3.
The binomial x-3 divides exactly the polynomial x^3-2x^2+cx-12 and c is a whole number then c is what?
2 answers
See http://faculty.ed.umuc.edu/~swalsh/Math%20Articles/Synthetic%20Division.html