Respuesta :

20. because 100/5=20cm2

Answer:

800

Step-by-step explanation:

Set up your proportion first (6/20 = 72/x). Then, square 6 and 20 (36/400 = 72/x). Cross multiply and divide (36x = 28800). Divide 28800 by 36 and that gives you 800 as your answer.