when you have a variable and an exponent in a fraction like this problem you subtract from top exponent to the bottom
so...
16r^6 divided by 8r^2 is 2r^4 because 16/8 = 2 and r^6/r^2 = r^4 (take the exponents and subtract from top to bottom: 6-2 =4 and then don't forget to add the variable r to the answer.
s^3/s^6 = s^-3 so it would go to the bottom of the fraction to avoid any negative exponents in the fraction.
