Solve the following related rates.
a) A potter forms a piece of clay into a right circular cylinder. As she rolls it, the height h of the cylinder increases and the radius r decreases. Assume no clay is lost. The height is increasing by 0.9 cm/ second. What it the rate at which the radius is changing when the radius is 4cm and the height is 7 cm.
b) A particle is moving along the curve y=5sqrt(4x+5). As the particle passes through the point (5, 25), its x coordinate increases at a rate of 4 units per second. Find the rate of change of the distance from the particle to the origin at this instant.