For the left side of the chart you would have to add 11 since his cousins age will always be 11 years more than his.
For the right side of the chart you would subtract 11 since his age is always 11 less than his cousins.
For the first row, 21 - 11 = 10, so you would fill in 10
For the second row, 14 + 11 = 25, so you would fill in 25.
Etc, etc.
