6. Anne loaned Donna's son David money to start a business, which later failed. David offered to sign a promissory note for the debt to prevent Anne from insti- tuting legal proceedings against the remaining assets of the failed business. Anne agreed, but would only accept a note cosigned or endorsed by Donna. Donna signed the back of her son's note. Anne sued Donna to collect the note when David could not be located. Is Donna liable? Why