In a city school of 900 students, 30% of the students are on the honor roll, 70% have a part-time job, and 25% are on the honor roll and have a part-time job. What is the probability (rounded to the nearest whole percent) that a randomly selected student is on the honor roll, given that the student has a part-time job?
18%
21%
43%
36%
Don't even know where to start...help