Unity script error C#

So I dont know what is happening here

Its clearly assigned to if you see at the top it says _cost from Upgrade11 button has been assinged to _cost1 same thing for the other four warnings

All we can see at the top is that you assign the value of _cost1 to Upgrade11._Cost, not that you actually assign a value to _cost1 itself.
But, assuming that the reason why you’ve declared these variables as public is to enable them to be serialized and you’re setting a value in the inspector, you can safely ignore the warning.