6. A registrar's office finds that the number of inkjet cartridges, I, required each year for its copiers and printers varies directly with the number of students enrolled, s. a. Find an equation of variation that expresses I as a function of s, if the office requires 18 cartridges when 2,900 students enroll. b. How many cartridges would be required if 3,100 students enrolled? (round to the nearest integer as needed)