To answer this question you need to know that the box and whisker plot take the data set and represent it fourths. Each section (half of the box or each whisker is 25% of the data.
So, for the 2 year old boys, half of them or 50% of the shoe sizes were 6 or less (40) and for the 3 year olds it was 1/4 or 25% of them (1/4 x 60= 15).
40-15= 25 more two year olds have a shoes size of 6 or less.
