U=X^0.5Y^0.5

I=100 X=$19 Y=$18 price of X=$23 (higher than before)

1. find income and substitution effect from price getting higher than before for two utility functions
2. pure exchange economy: illustrate edgeworth box with contract curve, find endowment point, is it pareto efficient? which part can mutually benefit?
3. if in competitive equilibrium, find optimal consumption bundle as price ratio function for total endowment
4. find competitive equilibrium starting from endowment point, find equilibrium consumptions, price ratios, and consumers' utility levels.