When Alexander moved into a new house, he planted two trees in his backyard. At the time of planting, Tree A was 36 inches tall and Tree B was 21 inches tall. Each year thereafter, Tree A grew by 6 inches per year and Tree B grew by 9 inches per year. Let AA represent the height of Tree A tt years after being planted and let BB represent the height of Tree B tt years after being planted. Write an equation for each situation, in terms of t, t, and determine which tree is taller after 3 years.