Quellos AS has the following relationship between costs in NOK million and the amount of production in number of units:

Production quantity 0 1000 2000 3000 4000 5000 6000 Costs 9 10 10,9 11,7 12,4 13 13,5

a) How large are the company's variable costs when the production quantity is 4,000 units? b) What are the company's fixed costs?

c) Are Quello's variable costs underproporctional, proportional, or overproporational? d) Explain briefly (max two sentences) what may be the cause of overproporative and underpropormal variable costs?