320*（1.25+2.5+1）
=320*1.25+320*2.5+320*1
=40*8*1.25+80*4*2.5+320
=40*（8*1.25）+80*（4*2.4）+320
=40*10+80*10+320
=400+800+320
=1520 320*（1.25+2.5+1）
=320*1.25+320*2.5+320*1
=40*8*1.25+80*4*2.5+320
=40*（8*1.25）+80*（4*2.4）+320
=40*10+80*10+320
=400+800+320
=1520