Since it must include the point (9,-12) we know that if we substitute x=9 and y=-12 into y = kx we will have a true equation, so we do that: y = k·x -12 = k·9 -12 = 9k We divide both sides by 9 to solve for k: = = k So the constant k is , and so we substitute that for k in y = k·x and get the answer: y = x
hope this helped good luck! :)