Sue Starr, a minor both in fact and appearance, bought on credit and took delivery of a telescope from 30-year-old Paul Prism for an agreed price of $100. Upon reaching her majority soon thereafter, Starr encountered Prism and said, "I am sorry for not having paid you that $100 for the telescope when the money was due, but I found out it was only worth $75. So I now promise to pay you $75." Starr subsequently repudiated this promise and refused to pay Prism anything. For this question only, assume that Starr bought the telescope from Prism after reaching her majority and promised to pay $100 "as soon as I am able." What effect does this quoted language have on enforceability of the promise? 
None. It makes the promise illusory. It requires Starr to prove her inability to pay. It requires Prism to prove Starr's ability to pay.