33 is the denominator. You can find this with the like terms. Putting 6/11 and 18/? Side by side, yo can see that 6 and 18 have a GCF of 6. You can use this to establish that 6 x 3 is 18. If you do something to the numerator, you just do it to the denominator to make it equal. So, with 6x 3, 11x 3 happens as well. So 6/11 is equal to 18/33