Answer:
Step-by-step explanation:
1.) 6
2.) A
3.)5
Divide each by 5 , now it is 7 over 9
So you reversed the subtraction a bit; the equation you're gonna be solving is

.
First step ya gonna do is to reverse the + and - symbols in the trinomial thats in the parentheses so your equation looks like

Now just combine like terms and your answer should be
5 years because when you divide 90 by 18 to get how many years it takes the tree to grow to 90 inches tall, you get 5.