[求助]请教两道数学题？

A photographer
            will arrange 6 people of 6 different heights for photograph by placing them in two rows of three so that each person in the first row is standing in front of someone in the second row.  The heights of the people within each row must increase from left to right, and each person in the second row must be taller than the person standing in front of him or her.  How many such arrangements of the 6 people are possible?

A.     5

B.     6

C.     9

D.     24

E.      36

选A

At a certain supplier, a machine of type A costs $20,000 and a machine of type B costs $50,000.  Each machine can be purchased by making a 20 percent down payment and repaying the remainder of the cost and the finance charges over a period of time.  If the finance charges are equal to 40 percent of the remainder of the cost, how much less would 2 machines of type A cost than 1 machine of type B under this arrangement?

(A) $10,000

(B) $11,200

(C) $12,000

(D) $12,800

(E) $13,200

选E