This sounds like only part of a problem. Please state the entire problem, and also tell us what you have tried so we can see what help you need.
If you need a hint, it might be useful to find the sum of the sizes for each set of units mentioned. How is that related to the average?
Good work, and just where my hint was meant to take you.Hi thanks for the help! Actually, that's the entire question. I was able to figure it out already but thanks anyways!!!! I needed to do ((5*20)+ (13*77))/18 to get the overall average size.