1 feet = 12 inches 
3 feets= 36 inches 
8 feets = 96 inches 
hope this helps 
Assume the year that it would take to these trees have the same height is : x (years) 
 
After x years, type A tree has heigth: 36 +23x (inches) 
 
After x years, type B tree has heigth: 96 +17x (inches) 
 
We have 36+23x = 96+17x 
Solve the equation, we have x=10 
 
Conclusion: It will take 10 years to these trees have the same height.