Sally sharpens knives in her spare time for extra income. Buyers of her service are willing to pay $2.50 per knife for as many knives as Sally is...

Sally sharpens knives in her spare time for extra income. Buyers of her service are willing to pay $2.50 per knife for as many knives as Sally is willing to sharpen. On a particular day, she is willing to sharpen the first knife for $1.75, the second knife for $2.25, the third knife for $2.75, and the fourth knife for $3.25. Assume Sally is rational in deciding how many knives to sharpen. Her producer surplus is