The overall average of the numbers is 50.
To find this, first multiply 3 and 80 together. This will give you 240. Next, multiply 9 and 40 to get 360. Add together 360 and 240 to get 600. Divide 600 by 12 (12 found by adding 3 and 9 together to account for all the numbers). 600 divided by 12 is 50. Thus making 50 the answer.
I hope this helps!