It's a squares.

（Ⅰ）求a的值；

（Ⅱ）假设同组中的每个数据用该组区间的中点值代替，估计该市中学生中的全体男生的平均身高；

（Ⅲ）从该市的中学生中随机抽取一名男生，根据直方图中的信息，估计其身高在180cm 以上的概率．若从全市中学的男生（人数众多）中随机抽取3人，用X表示身高在180cm以上的男生人数，求随机变量X的分布列和数学期望EX．

给农作物施用下列一种化肥就能增加两种需要量较大的营养元素，这种化肥是

Jack is a clerk of a bookstore. Here is the note from his boss, Ben. Jack has to decide what books to order according to the following note and the descriptions of the books.
Hi Jack,
You must hand in the order list of books to me by the first working day of every month. The rules for choosing books are:
For textbooks:
● August is coming. We must choose all textbooks, without thinking of other rules.
For books which are not textbooks:
● If more than five copies of books were sold last month, we choose them. But if there are five copies or more in stock (现货), we do not make an order.
● If the wholesale (批发) prices of the books are higher than $75, we do not choose them. And we do not order anything whose retail (零售) price is higher than $100.
Ben
The descriptions of the books