2. 16
This is because if you do keep change flip you will have 4/1*4/1 by keeping the four and just changing it into an improper fraction. Changing the division sign into a multiplication sign and then flipping the 1/4 to 4/1. Than your will simplify 4/1*4/1 is 16/1. Than if you simply 16/1 you will get just 16.
3. 5
This is the same thing but you will make the 1 2/3 into an improper fraction and that is by multiplying the 1 by the denominator (3) and then adding by the numerator. Making you get 5/3 and then using keep change flip you will have 5/3*3/1 making 15/3. Than simplifying into just 5. This is because 15 divided by 3 is equal to three.
4. 3
Same thing just use keep change flip. Than you have 3/5*5/1 and that is equal to 15/5 making it 3.
Hope this can make it easier for you to understand :)