Answer:
20 in Â
Step-by-step explanation:
Tree 1:
Rate of growth = (½ ft/2 yr)
 12 yr growth = 12 × (½/2)
            = 6/2
            = 3 ft
            = 36 in
Tree 2:
Rate of growth = (4 in/3yr)
 12 yr growth = 12 × (4/3)
            = 48/3
            = 16 in
Difference:
Tree 1 - Tree 2 = 36 - 16
              = 20 in
The trees will differ in height by 20 in.