4. (20 分)

Consider a pure exchange economy with two goods, X and Y. There are only two individuals in the economy, Individual A and Individual B, whose utility functions are defined as UA = √XAYA and UB = √XBYB, respectively. Individual A's endowment is eA = (XA, YA) = (40, 40), and Individual B's endowment is eB = (XB, YB) = (60, 10).

(1) Derive the contract curve. (5 分)