6 A closed, right-circular cylinder's radius is decreasing at a rate of 3 cm s-1 and its height is increasing at twice the rate of the radius. Determine how fast the cylinder's surface area is changing when its height is 10 cm and its radius is 12 cm. 7 Side a of a right-angled triangle is increasing at 5 cm s"], whilst side b of the triangle is decreasing at a rate of 4 cm s'1. Determine how fast the length of the hypotenuse h is changing when a = 15 cm and b= 20 cm