#### Answer

A: 3 boxes

#### Work Step by Step

First we will subtract 3.99 from 20 because that is the price of the milk. This gives us:
20-3.99=16.01
Now we will divide our difference by 4.39 in order to find the number of cereal boxes Mr Washington can buy.
16.01$\div$4.39 $\approx$ 3.64
Now since there is no such things as 3.64 boxes we go down to the nearest lowest integer in order to find the number of boxes Mr Washington can buy. That is 3 so Mr Washington can afford to buy 3 boxes of cereal.