Consider the rectangle in the first quaurant with its lower left vertex at the origin and upper right vertex at the point P. The x-coordinate of point P is increasing at a constant rate of 7
units per second, and the y-coordinate of point P is decreasing at a constant rate of 6 units
per second. At the instant when point P is at x = 3 and y = 4, what is the rate at which
the area of the rectangle is changed, in square units per second?