Each chicken lays 7 * 3 = <<7*3=21>>21 eggs a week
Each week all the chickens lay 21 * 8 = <<21*8=168>>168 eggs
In 4 weeks all the chickens lay 168 * 4 = <<168*4=672>>672 eggs
672 eggs equal 672 / 12 = <<672/12=56>>56 dozens.
Kelly would make 56 * 5 = <<56*5=280>>280 dollars
#### 280