{Total} = {First correctly} + {Second correctly} - {Both correctly} + {Neither correctly}
100 = 85 + 65 - {Both correctly} + 5
{Both correctly} = 55.
If 85 percent of the test takers taking an old paper and pencil GMAT exam answered the first question on a given math section correctly, and 65 percent of the test takers answered the second question correctly, and 5 percent of the test takers answered neither question correctly, what percent answered both correctly?

(a) 60 %
(b) 55 %
(c) 70%
(d) 75%
(e) 80%