Mara and Christina each have an income of $900 which they spend entirely on jeans and pairs of shoes. They exclusively buy a brand of jeans that sells for $75 a pair and shoes that sell for $50 a pair.

a. On two separate graphs, draw Mara and Christina's budget constraint with jeans on the y-axis.

b. What is the equation of the budget constraint? Provide nonmathematical interpretations of the y-intercept, x-intercept, and slope.

c. Draw an indifference curve for Christina showing that she optimally allocates her income to 12 pairs of shoes and 4 pairs of jeans. What is the ratio of her marginal utility of shoes to her marginal utility of jeans at.