Not sure what you’re asking, the title of the post says 40% milk fat whipping cream, but then you ask about 96% milk fat whipping cream. Well I don’t really know anything about whipping cream, but the math isn’t a problem. If the relationship between carb content and milk fat content in whipping cream is a linear relationship, then this can be solved using simple proportions. So, given your figures, a cup of whipping cream with 96% milk fat would have 7.24 g of carbs. There are 16 tbsp in a cup so there would be 0.45 g of carbs in 1 tbsp of 96% milk fat whipping cream.
Now if the relationship between milk fat and carbs in whipping cream is not linear, then one would have to have a math function that would express the relationship mathematically. I’m an engineer, not a nutritionist or dietitian (or whatever profession understands these kinds of things about food) so I have absolutely no idea if my assumption about linearity is true or not and so have no idea if my calculations above are correct or not.