If the number ends with an even number or a number that is always divisible by 2. Or every number that ends with 5 or zero is always divisible by 5 too. Bdause for example in a fraction we do 10/5 and it will be equal to 2/1 or 2. Hope it helped you!
You can do Guess and Check(but the smart way). You first get 102 and 12. Then, you can minus 3 from each one of them, getting 99 and 9, also being 11 times the other, so then the answer would be 180 - 99 or 90 - 9, equaling 81
