In a survey of 15,000 students of different schools, 6,000 of them were found to have tuition classes before the SEE examination. Among them, 3,000 studied only Mathematics, 1,800 only Science and 600 studied other subjects but not these two subjects. (i) If M and S denote the sets of students who studied Mathematics and Science respectively, write the cardinality of n (M), n (S) and n(MUS). (ii) Find the number of students who studied Science. (iii) What percent of the students of the survey studied either Mathematics or Science?​