Tutorial Exercise The length of a rectangle is increasing at a rate of 6 cm/s and its width is increasing at a rate of 4 cm/s. When the length is 10 cm and the width is 5 cm, how fast is the area of the rectangle increasing (in cm2/s)? Step 1 Let l and w represent the length and width of the rectangle in cm, and let A represent the area of the rectangle in cm2. Writing an equation for A in terms of l and w gives the following result. A =