What is the greatest common factor of 12a and 42a?

42 = 2 * 3 * 7 12 = 2 * 2 * 3 Hence gcf (42, 12) = 2 * 3 = 6 Notice that a is also a factor of 12a and 42a. Hence gcf (42a, 12a) = 2 * 3 * a = 6a