Add up the values in row 1 and row 2, which correspond to the groups "under age 12" and "13 to 30 years old" respectively
6+7 = 13 individuals under age 12
7+4 = 11 individuals 13 to 30 years old
13+11 = 24 people total from the two groups
There are 6+7+7+4+4+1 = 29 people total from the entire survey
So the final answer is 24/29. It cannot be reduced further.