Mrs. Gordon sometimes makes her melon salad for special events. When she made it a couple months ago, she used 3 pounds of honeydew melon and 7 pounds of
watermelon, which cost her $16. Today, she used 7 pounds of honeydew melon and 4
pounds of watermelon, spending a total of $25 on the melons. Assuming that the
prices of the melons haven't changed, how much does a pound of each type of melon
cost?