a and b together can do a work in 6 days . if a alone can do it in 15 days . in how many days can b alone do it ?
"1 / 6 – 1 / 15 = 1 / 10 = > 10 answer : a"
add(inverse(subtract(divide(const_1, 6), divide(const_1, 15))), divide(const_2, add(const_2, const_3)))