When Paisley moved into a new house, she planted two trees in her backyard. At the time of planting, Tree A was 21 inches tall and Tree B was 33 inches tall. Each year thereafter, Tree A grew by 6 inches per year and Tree B grew by 3 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, and determine the interval of time, t, when Tree A is taller than Tree B.