.4 A store sells two sizes of mattresses: queen and king. It buys q queen mattresses at x dollars each, and k king mattresses at z dollars each. For each situation, write an equation solved for the given quantity. The equations may contain more than one variable; you may not get a numeric answer. a) The number of queen mattresses the store can purchase if it spends a total of $50,000 on mattresses and buys 40 king mattresses for $400 each.