What's "by" mean here and when's it used like this?

Native speaker’s answer
Rebecca
"By" is preposition that in this case, is used with a verb to indicate the amount or size of a margin or number difference. Here, it's used to express that home product sales increased significantly (by double digits, which means more than 10%). Ex: Net sales increased by 18% in the last six months. Ex: My salary has decreased by 30% due to inflation.