$15+20-30=5$ 
$$30$$ children going to Adventure Park took part in at least one of two events. $$15$$ of them took part in the "moving bridge" contest, and $$20$$ of them went down the zip-wire. How many children from Adventure Park took part in both events? ($$2013$$ Math Kangaroo Problems, Level $$3-4$$, Question \#$$14$$) 

(A) $$25$$ 
(B) $$15$$ 
(C) $$30$$ 
(D) $$10$$ 
(E) $$5$$ 