In a group of 60 students, 18 students take algebra i, 20 students take algebra ii, and 10 students take both subjects. how many students don't take either of these subjects?

Out of the total 60 students 18 take Algebra 1 and 20 take Algebra II. 10 take both. So out of the 18 taking algebra 10 are taking Algebra II. If we don't count that 10 because they are already counted in Algebra II count.  So 28 students are taking either course. Therefore 60-28 = 32 students who are not taking either of these courses

Sin Ф=opposite / hypotenuse
tan Ф=opposite / adjacent.
cos Ф=adjacent /hypotenuse.

In this case:
sin yº=a/6

opposite=a
hypotenuse=6

tan yº=a/b

opposite=a
adjacent=b

cos yº= adjacent /hypotenuse=b/6

cos yº=b/6