450-450÷18x15
=450-25x15
=450-375
75
4/15÷（13/9-2/3x5/6）+5/6
=4/15÷（8/9)+5/6
=3/10+5/6
=17/15
不懂的欢迎追问,如有帮助请采纳,谢谢!