what number can you divide both the divisor and denominator by?
i see that 12 and 126 are divisible by 1, 2, 3, and 6
we're going to choose the biggest number we can divide by (which is 6)
12/6=2 / 126/6=21
the answer would be 2/21 because there is no other number (other than 1) that you could divide these both into