Assume that product Z is made of two units of A and four units of B. A is made of three units of C and two units of D. D is made of two units of E. Currently we have two units of Z, two units of A, two units of B, four units of C, four units of D, and ten units of E. If an order for 12 units of Z is received, how many additional units of E are needed to fulfill this order?
(Hint: draw the product tree, mark the amounts available, and systematically move down from Z to see how many extra are needed)