if a , b and c together can finish a piece of work in 4 days . a alone in 12 days and b in 18 days , then c alone can do it in ?
"c 9 days c = 1 / 4 - 1 / 12 – 1 / 18 = 1 / 9 = > 9 days"
divide(const_1, subtract(subtract(const_0_25, divide(const_1, 12)), divide(const_1, 18)))