well, the price difference is 60000 - 40000 = 20000.
so, we're told that the price increase acres wise is 800 bucks per acre, but we also know it's a total of 20000, so how may times does 800 go into 20000?
20000 ÷ 800 = 25.
so we know that in 20000 bucks there are 25 acres, so how many will there be in 60000 bucks?