a is twice as good a workman as b and they took 6 days together to do the work b alone can do it in .
"wc = 2 : 1 2 x + x = 1 / 6 x = 1 / 18 = > 18 days answer : a"
multiply(divide(multiply(6, add(const_2, const_1)), const_2), const_2)