Help to make a bubble chart

I am very new to Excel. If my question is too simple, I apologize.

I have data that looks like this:

London,item1,25
London,item2,30
London,item3,20
Chicago,item1,15
Chicago,item4,20
Chicago,item5,25
Chicago,item6,35
Chicago,item7,5
Los Angeles,item3,40
Los Angeles,item5,5
Los Angeles,item8,5

I want to make a bubble chart that will show the city and the item as one axis and the count as the bubble - i.e., add up for London the 25,30,and 20 for a total of 75, and then show that item1 is 33% of the total as the bubble. Is there a way to have Excel to add up all of the items in column 3 that have the same value in column 1, then divide each entry to get the percentage?

I'd also like to be able to show each item as it's own bubble. Is that possible in the same chart, or would it need to be two different charts?

Thank you for any help.

smna

But, I have thousands of lines of this data, so if I can automate the calculations, that would be great.