Tutorial Exercise The length of a rectangle is increasing at a rate of 4 cm s and its width is increasing at a rate of 9 cm s When the length is 8 cm and the width is 6 cm how fast is the area of the rectangle increasing in cm s Step 1 Let and w represent the length and width of the rectangle in cm and let A represent the area of the rectangle in cm Writing an equation for A in terms of and w gives the following result A