Determine whether each quadrilateral must be a parallelogram & justify your answer.

Bill makes leather shoes. he charges $45 for a pair of women's shoes and $50 for a pair of men's shoes. he sells x pairs of women's shoes and y pairs of men's shoes each week and earns a total income of $2,500. this situation can be represented by the equation . if bill has no female customers during a particular week, he needs to sell pairs of men's shoes to earn his weekly income of $2,500.