Take into account that the relation in between the age of the tree and its tall can be written as follow:
y = kx + 13
where x is the age, y the tall and k the constant of proportionality.
You can calculate the value of k by using the given information in the statement of the question:
k = 14 in/year
To determine what is the age of the tree when it is 97 in tall, solve the linear equation for x:
x = (y - 13)/k
replace y = 97 and k = 14
x = (97 - 13)/14 = 84/14 = 6
Hence, the tree is 6 years old when it is 97 inches tall