Problem: a is twice as good a workman as b and they took 9 days together to do the work b alone can do it in .
Rationale: "wc = 2 : 1 2 x + x = 1 / 9 x = 1 / 27 = > 27 days answer : e"
annotated_formula: multiply(divide(multiply(9, add(const_2, const_1)), const_2), const_2)