A hay farmer harvested 560 bales of hay from 5 acres of grass per month last year. This year, he planted an additional 7 acres of grass. If the farmer also owns 9 horses and each horse consumes 3 bales of hay a day, how many bales of hay would the farmer have left by the end of December if he starts feeding them this year's hay beginning the first day of September?
For every acre of grass, the farmer can harvest 560/5 = <<560/5=112>>112 bales of hay each month.
This year, the farmer has 7 + 5 = <<7+5=12>>12 acres of grass.
He can expect to harvest 12 x 112 = <<12*112=1344>>1344 bales of hay per month.
The total hay production this year is 1344*12 = <<1344*12=16128>>16128
From September to December, the farmer would have to feed his horses for a total of 30 + 31 + 30 + 31 = <<30+31+30+31=122>>122 days
Each day his horse eats a total of 3*9 = <<3*9=27>>27 bales of hay.
For the 122 days, the horses will eat a total of 27*122 = <<27*122=3294>>3294 bales.
The total number of bales remaining will be 16128-3294 = <<16128-3294=12834>>12834.
#### 12834