Answer :

If you take 9x4 you get 36 and multiply that by 2 (it's 2 because 4x2 is 8) you get 72

If you take 9x8 you get 72
It can help you explain 9x8 because 9x4 equals 36. 4 is the half of 8. So you would do 36 + 36 which equals the product of 9x8=72.