Mrs. Hancock sometimes makes her melon salad for special events. When she made it a couple months ago, she used 1 kilogram of honeydew melon and 1 kilogram of watermelon, which cost her $3. Today, she used 3 kilograms of honeydew melon and 1 kilogram of watermelon, spending a total of $5 on the melons. Assuming that the prices of the melons haven't changed, how much does a kilogram of each type of melon cost?​