"Her bag is light."
Translation:Son sac est léger.
Except that "un sac" is just a "sack" or a "bag", not actually a purse. A purse (e.g., handbag) would be "un sac à main", "un portefeuille" (i.e., a wallet used by a woman would be called a purse), or "un porte-monnaie", a (coin) purse; un sac à bandoulière = a shoulder bag.
When I was doing the excercise there was one before that said to translate her bag is big. I put son sac est grande. It said it was wrong not only for grande but son was wrong too they put ton sac est grand. Does that mean son sac est grand is wrong. This time on this one I put ton instead of son. I put ton sac est léger. Why wasnt this accepted?
One use of "une bourse" is "un porte-monnaie", a (coin) purse. But a "bag" or "sack" (i.e., un sac) is not a purse. A purse can be un sac à main, un portefeuille, un porte-monnaie, (coin) purse, or un sac à bandoulière (shoulder bag/purse). But "un sac" is just a sack or a bag, not a purse. http://www.wordreference.com/fren/sac