4. Mary considers spoonfuls of sugar (S) and spoonfuls of medicine (M) to be perfect substitutes and always requires 10 spoonfuls of sugar to be willing to give up 3 spoonfuls of medicine (Notice that it means the spoonful of medicine is more valu- able for Mary than spoonful of sugar). Suppose sugar costs $2 per spoonful whereas medicine costs $6 per spoonful. Mary's income is $72. Mary's utility function can be expressed as and her optimal bundle is (a) U(S,M)=108 + 3M; 0 spoonfuls of sugar and 12 spoonfuls of medicine (b) U(S,M)=38 + 10M; 0 spoonfuls of sugar and 12 spoonfuls of medicine (c) U(S,M)=108 + 3M; 36 spoonfuls of sugar and 0 spoonfuls of medicine (d) U(S,M)=38 + 10M; 36 spoonfuls of sugar and 0 spoonfuls of medicine (e) None of the above