Point A's coordinates at time t are (9 - 3t, 0), and point B's coordinates are (0, 6 + 2t).
The distance d between the two points at time t is
d(t) = √((9 - 3t)² + (6 + 2t)²) = √(13t² - 30t + 117)
so that at t = 1, the distance between the two points is 10.
The distance changes at a rate of
dd/dt = (26t - 30) / √(13t² - 30t + 117) units/sec
so that at t = 1 sec, the distance is changing at a rate of
dd/dt (1) = -1/5 units/sec
