The bottom side of the smaller rectangle is marked 10, and the bigger one is marked 20. 20÷10=2, making this a 2:1 scale. Simply multiply the 8 on the right of the smaller rectangle by 2 and you'll get 16, the answer for the similar rectangle.
Since the rectangle on the left is 10 cm and the one on the right is 20, that means that it was multiplied by 2. So you multiply 8 by 2 and you get 16.
