frosty the snowman was made of 3 snownballs placed on top of each other. The middle and top snowballs radii are 1/2 and 1/4 the radius of the lower...

frosty the snowman was made of 3 snownballs placed on top of each other. The middle and top snowballs radii are 1/2 and 1/4 the radius of the lower ball, respectively. Frosty the Snowman knew the sun was hot that day , he was melting down such that his volume was decreasing in a rate of 144pi in^3 per second. What is the rate of change of the radius of the loweer ball at moment when the radius of the middle ball is 12in?