i'm going to increase the size of my kitchen by six feet .这里的 by 启什么作用

by是用来描述大小的
这句话是说某人想扩大厨房的面积，扩大6尺
数学中，这个by也是加法的意思
比如说，incresase 8 by 10就是8加10

原问： i'm going to increase the size of my kitchen by six feet .这里的 by 起什么作用？
回答：by six feet 是介词短语。用作状语，表示程度。可以翻译为：达到六英尺长（宽）。by 在这里的意思是：to the extent of (sth) 达到...的程度。
全句可以翻译成：我要把厨房的面积增大六英尺。

by的这种用法所起到的作用就是描述：to the extent of (sth)例如：The bullet missed him by two inches.那子弹差两英寸就打中他了.The carpet is too short by three feet.那地毯短了三英尺.It would be better by ...

请看by的用法
by：
○1在…旁边。如 There is a school by the river.
○2到…为止。如 I will be here by 5:00.
○3被。如 This machine was mended by my father.
○4经过。如 The boy ran by the stop.
○5依据；按照。如 What time is it by your watch?
○6由于。如 I took the magazine by mistake.
○7乘坐。如 They traveled by plane.
○8表示方法、手段，“靠，通过”。如 He makes a living by selling vegetables.
○9表示相互差距。如 increase by 30% (增加30%)；miss the train by ten minutes (晚十分钟没赶上火车)
注：by还有副词的意思，见以下两条：
○10在旁边。如 He lives by.
○11经过；过去。如 She walked by.
你给的句子应该是第9条用法！在实际翻译中，这种用法by常不翻译
“我打算把厨房增加6英尺。”