The correct answer is:
l = 65 – 15d; discrete
15 is the centimeters he cuts off every day, you have to multiply that by D that´s the nomber of days, in order to calculate how much baguette does he have left.
If 4 days have passed, the anser would be 5 centimeters:
I=65- 15(4)= 65-60= 5