Given
Number of bags the family bought = 6 bags
Each bag has 14 cookies
They had eaten 29 of the cookies
The total number of cookies available in the 6 bags can be found using the formula below:

Substituting the given values:

Let the number of cookies they have left be x
The number of cookies left is the difference between the total number of cookies and the number they have eaten

Substituting we have:

Hence, they have 55 cookies left