Answer:
720
Step-by-step explanation:
I will use the following counting principle:
Product rule: if there are n ways of doing something, and m ways of doing another thing, there are n×m ways of doing both things.
First, we have to choose the 3 people that will be in the first row. This is a 3-element subset of the set of six people, therefore there are ways of doing this.
Now, we have to arrange the order of the 2 lrows. Each one has 3 people, so there are 3!=6 ways to form one rows. Hence, there are 3!²=36 ways of arranging the two rows.
By the product rule, there are 20×36=720 ways of arrange the officers.