The correct answer for two-fifths of Three-sevenths is 29 over 35. For a full explanation visit bbc.co.uk/bitesize/standard/maths_ii/numbers/fractions/revision/4/

When starting out with two wholes, that makes 2*(7/7) or fourteen sevenths. Three seventh, or 3/7 is then added. Fourteen plus three makes for seventeen sevenths.