so each cereal box has 4 2/3 ounces of cereal, or 14/3 ounces (just changing the integer to fraction)
for a), we have to divide 81 by 14/3 like this:
in decimals, 243/14 = 17.35
so, for a), we have that 17 full boxes of cereal can be made
for b), you have to look at the decimals of the last division
We have that .35 of cereal was left out, which is the same as 35/100 or 7/20