"earn in" is a correct and usable phrase in written English.
It means to earn or make money within a specific time period or context. Example: "I was able to earn in a month what I used to make in a year at my previous job."
Factory workers earn in a day what their American counterparts earn in an hour.
"They can earn in a few catches what they would normally earn in a year".
You get what you earn in this game.
That's more than I earn in a year.
Academic managers can earn in excess of £40,000.
What rugby players earn in Europe is very rarely divulged.
They can earn in a year here what could take them up to a decade to earn in China.
Prostitution at least offered financial independence: a typical harlot could earn in a month what a tradesman or clerk would earn in a year.
A doctor from one of those countries can earn in two days in the UK what it will take him to earn in a month at home.
I made more money during my lunch hour than you'll earn in a decade.
What did he and the truck earn in a typical year?
