Problem: a and b can do a piece of work in 10 days . with the help of c they finish the work in 3 days . c alone can do that piece of work in ?
Rationale: "c = 1 / 3 – 1 / 10 = 7 / 30 = > 4.3 days answer : b"
annotated_formula: inverse(subtract(3, divide(3, 10)))