Answer:
6 years (assuming the question is how many years it'll take for them to be the same height)
Step-by-step explanation:
You have to first convert the height of the trees into inches. 7 feet will convert into 84 inches and 8 feet will convert into 96 inches. since type a is 84 inches and grows 11 inches a year it'll create the expression 84+11x. Type b will create the expression 96+9x. Since you're looking for how long it'll take you set the expressions up to one another and solve for it.
84+11x=96+9x
-84 -84
11x=12+9x
-9x -9x
2x=12
x=6