Since we know 85% of the students participated last year we can assume the same amount will participate this year so to find the answer you simply do the total number of students (320) multiplied by 85% or .85 to get the best guess of how many students will participate this year.
First you would have to multiply (1200)(3%)(7) which would be 252.then you add what jamie invested and 252. therefore she would have $1452 in his account after 7 years.