The length x of a rectangle is decreasing at the rate of 5 cm/minute and the
width y is increasing at the rate of 4 cm/minute When x = 8cm and y = 6cm, find
the rates of change  of (a) the perimeter, and (b) the area of the rectangle 8 A balloon, which always remains spherical on inflation, is being inflated by pumping
in 900 cubic centimetres of gas per second