Hello, I'm Kate. This is a photo of my aunt's family. The woman in the photo is my aunt, Jane. She is a teacher and she is very kind（善良）. These are my cousins Jeff and Jack. They are seven and they are twins. Look! That lovely baby is my aunt's little daughter, Rose. She is only one. I love them very much.

某企业今年5月份产值为a（1﹣10%）（1+15%）万元，比4月份增加了15%，4月份比3月份减少了10%，则3月份的产值是____ 万元．

（Ⅰ）求a，c的值；

（Ⅱ）求sin（B﹣C）的值．

如图所示，用长10m的铝合金条制成下部为矩形，上部为半圆的窗框（包括窗棂）．若使此窗户的透光面积最大，则最大透光面积为（）