So we can see they are the same shape. This means that it is a scaled drawing and each side is scaled up. If 4 goes into 10 2 1/2 times then that means we can divide also 10 by 2 1/2 to get 4. So we can use the same method for 16. We can divided 16 by 2 1/2 to get the answer:
16/2.5 = 6.4 (cm)