Xavier and Ying are partners in a course project. Xavier is the project leader and thus is the first to decide how many hours, h Subscript Upper X, to put into the project. After observing the amount of time that Xavier contributes, Ying decides how many hours, h Subscript Upper Y, to contribute. Xavier's utility function is Upper U Subscript Upper Xequals20(h Subscript Upper X Baseline plus h Subscript Upper Y Baseline )Superscript 0.5minush Subscript Upper X, and Ying's utility function is Upper U Subscript Upper Yequals20(h Subscript Upper X Baseline plus h Subscript Upper Y Baseline )Superscript 0.5minush Subscript Upper Y. Ying threatens not to work on the project. For Ying's threat to be credibleLOADING..., what is the smallest number of hours that Xavier must contribute to the project? For Ying's threat to be credible, Xavier must work at least nothing hours on the project. (Enter a numeric response using an integer.)