What are the marginal cost and marginal revenue (or total cost and total revenue) for producing plastic when?

Question

oil is $65/barrel and $85/barrel? All other things being equal! Or does anyone know where I can get this info? I can't find a good enough source online.

Answer 1

To truly answer your question specifically (to give values for MC and MR) we would need to see the production function for plastic.  But here is the answer, in general:

When the cost of an input goes up, the total cost of producing increases and the cost of producing one extra unit (the marginal cost) also increases.  WITHOUT A CHANGE IN PRICE (i.e., all else being equal), marginal revenue and total revenue will fall.