It said the sale earned OVER $25 from selling cookies at $3 dollars each so if we let r=revenue , p=price per cookie and c=number of cookies sold:
pc>r and since p=3 and r=25
3c>25 divide both sides by 3
c>25/3
Since cookies are quantized units, they must be integers so:
c>8 1/3
c≥9 or in interval notation
c=[9, +oo)