20. The length of a rectangle is increasing at a rate of 5 cm/sec and the width is decreasing at a rate of 2 cm/sec. At what rate is the area changing when length is 12cm and width is 4cm? 21. A rectangle is drawn in the first quadrant so that its base is on the x axis and its left side is on the y axis. What is the maximum area of this rectangle if its upper right vertex lies on the line segment connecting the points (4,0) and (0,8)? 22. Suppose the velocity of a particle moving on the number line is given by v(t) = 6t-4t for 10. If the initial velocity is 0 and the initial position is the origin a) Find the acceleration when t-2. b) Find the position of this particle when t=2. 23. Find two numbers whose sum is 10 and the sum of their squares is a minimum.