Logic/Economics problem

This is a cool problem I just came across the other idea. It's basically a logic problem that describes economic logic (most importantly, the Coase Theorem). So, I thought I'd see how ya'll skeptics do when facing a problem like this. Like I said before, I think skeptics should add economics to their 'skeptical toolbox'

There are three industrial firms in Happy Valley.

Firm Initial Pollution Level Cost of Reducing Pollution by 1 Unit

A 70 Units $20
B 80 Units $25
C 50 Units $10

The government wants to reduce pollution to 120 units, so it gives each firm 40 tradable pollution permits.

a. Who sells permits and how many do they sell? Who buys permits and how many do they buy? Briefly explain why the sellers and buyers are each willing to do so. What is the total cost of pollution reduction in this situation?

b. How much higher would the costs of pollution reduction be if the permits could not be traded?

give it your best shot - winner gets mad props