Please help, I suck at math. The Life of Trees Project

Part A: Tree Research
Five years ago your teacher planted a tree that was 24 inches tall and has tracked it's growth. You decided you want to plant a tree seed and see when both trees will be the same height.

Teacher:
Hickory (Shellbark)
10'' per year
80' when mature

Me:
White Ash
18.5'' per year
65' when mature

Part B:
Write a linear equation for each tree to represent it's growth each year. Fill in the following info to help.

Identify your variables:
x = y=

What are the variables? (find the let statement)​