"Lorenzo lives on X and Y only. His utility function is U (X,Y) = min(3X+4Y; 7Y). The prices of both goods are positive. He will:

a. Never buy more X than Y;

b. Always buy equal amounts of the two goods;

c. Always buy more Y than X;

d. Always buy more X than Y;

e. More than one of the above is true."

The right choice is a. But why not b? Thank you