a cistern is normally filled in 12 hours but takes two hours longer to fill because of a leak in its bottom . if the cistern is full , the leak will empty it in ?
"1 / 12 - 1 / x = 1 / 14 x = 84 answer : b"
inverse(subtract(divide(const_1, 12), divide(const_1, add(12, const_2))))