3. Tarzan went to the plant nursery and bought a tree that was initially 90 feet tall for his monkey friends to climb on. 
 After planting the tree, Tarzan made a table to record the height, h, of the tree, t years after it was planted. “Zero” is the time when he planted the tree.
 t 0 1 2 3 4
 h 90 105 120 135 150
 (a) Use words to describe the relationship between the height of the tree and the number of years since it was planted. 
 (b) Write a two-variable equation to illustrate the relationship between the height of the tree and the number of years since it has been planted.