天山-6-19,25好像没有讨论过

Q19:

A total of $60,000 was invested for one year. But of this amount earned simple annual interest at the rate of X percent per year,and the rest earned simple annual interest at the rate of Y percent per year. If the total interest earned by the $60,000 for that year was $4080,what is the value of X?

(1) X=(3/4)Y

(2) the ration of the amount that earned interest at the rate of X percent per year to the amount that earned interest at the rate of Y percent per year was 3 to 2.

ANS:C

A+B=60000, X%A+X%B=4080

(2)A/B=3/2, A=36000,B=24000, (1)X%36000+(4/3)X%24000=4080

Q25:

A photograher  will arrange 6 people of 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 rigth,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

ANS:A

123        124         125          134          135

456        356         346          256          246

how to get these two answers?

Thank you!!