Answer: 16 square units
Explanation:
Since there are units, you see how much units there are on all the sides of the rectangle, which is 5 for the length, and 3 for the width. you then double it, so 10 and 6, because 5 units for one of the long sides, and 3 units for one of the short sides. so then you add 10 and 6, which is 16.
Sorry if I overexplained.