a and b together can do a work in 6 days . if a alone can do it in 42 days . in how many days can b alone do it ?
"b 7 1 / 6 â € “ 1 / 42 = 1 / 7 = > 7"
add(inverse(subtract(divide(const_1, 6), divide(const_1, 42))), divide(const_2, add(const_2, const_3)))