It's possible mathematics in a ListBox?

[Tamgovb]

Hi All

It's possible adding a different of values in a ListBox. For example. I have in a ListBox some a value 5 then I add other the value 3. If will be the same of item this should add only an value, and the name of item should be the same also the quantity of thing should stay the same.

e.g.

I have an item:

Fish 5

I want to add:

Fish 3

it should still be only 1st thing, but only quantity should change, it's possible something this?

I would have then:

Fish 8

Thanks in advance