Line A and Line B are increasing at constant rates. The initial height of Line A is 2 feet. The initial height of Line B is 3 feet. The height of A after x = 1 (or 1 minute) is 6 feet. The height of B at x = 1 (or 1 minute) is 3 1/2 feet. What will be the height in feet of each line at x = 4 (after 4 minutes)? Give a mathematical explanation