1 Rosaline is not maximazing her utility because the marginal utility per dollar is not the same for sandwiches and juice.Sandwiches have higher utility than juices.
Marginal utility per dollar for sandwiches
"Marginal utility \\over price"
Marginal utility for juice
2 .To reach an equilibrium ,rosaline should consume more of juice because it has a higher marginal utility per dollar.If he continues to consume juice she will reach a point of diminishing marginal return till it is equal to marginal utility for sandwhiches.
3.Thislevel is of marginal utility is maximazing because the marginal utility per dollar is equal for both sandwhich and juice.
Marginal utility per dollar for Juices