a can do a half of certain work in 70 days and b one third of the same in 35 days . they together will do the whole work in .
"a = 140 days b = 105 days 1 / 140 + 1 / 105 = 7 / 420 = 1 / 60 = > 60 days answer : d"
add(inverse(multiply(70, const_2)), inverse(multiply(35, const_3)))