(a) Consider the expenditure function (x, y,) = x^0.5y^0.7U, where > 0. Determine whether this function is a valid expenditure function.

(b) Consider an individual who consumes only two goods, and . She cannot borrow money and does not save money. Her Marshallian demand functions are x^m= 0.8 (m/Px) and ^m = 0.57, where x and y are the prices of goods and respectively and is her income. Determine whether this set of demand functions is valid.