In a class of 40 students; 30 have taken science; 20 have taken mathematics and 8 has neither taken mathematic nor science. Find how many students have taken: i) both subjects. ii) exactly one subject

In a class of 40 students; 30 have taken science; 20 have taken mathematics
and 8 has neither taken mathematic nor science. Find how many students
have taken:
i)  both subjects.
ii) exactly one subject