A Building in the Shape of a Rectangular Box Is

Multiple Choice

A building in the shape of a rectangular box is to have a volume of 6,000ft³ (see the figure) . It is estimated that the annual heating and cooling costs will be $2/square foot for the top, $3/square foot for the front and back, and $2/square foot for the sides. Find the dimensions of the building that will result in a minimal annual heating and cooling cost. What is the minimal annual heating and cooling cost(C) ? ​ ​

A) x = 30; y = 20; z = 10; C = 3,500
B) x = 20; y = 30; z = 30; C = 3,500
C) x = 30; y = 20; z = 20; C = 3,600
D) x = 20; y = 30; z = 10; C = 3,600