A college in Thrissur has four clubs: Dance, Debate, Quiz and Art. How many students belong to exactly two of the clubs?

The six exactly-two regions hold $4+3+5+6+2+7=27$. 39 is the exactly-one total, 10 the exactly-three total $1+3+2+4$, and 30 wrongly adds the 3 in the centre (all four clubs).