Help me solve the following problems. Show illustrations. Thank you! Two parallel sides of a rectangle are being lengthened at the rate of 20 mm/sec, while the other two sides are shortened in such a...

Help me solve the following problems. Show illustrations. Thank you!

Two parallel sides of a rectangle are being lengthened at the rate of 20 mm/sec, while the other two sides are shortened in such a way that the figure remains a rectangle with a constant area of 5000 sq mm. What is the rate of change of the perimeter P when the length of the increasing side is 50 mm.