What does this mark scheme mean?

For (b).
Mark scheme for
2 marks: explanation of possible economics/diseconomies
4 marks: development with explicit indetification of chabge of scale/appropriate explanation/long run change

How would i go about answering to get the 4 marks? I dont unserstand what the mark scheme is saying

I believe it may be referring to returns to scale?

What exam board are you?
Also i assume you're A2 Econ?

A2 yeah. WJEC
My teacher has never mentioned the term 'returns to scale' so idk if I have to know it. Havent seen it on the new spec

I teach WJEC and although the specification does not state the requirement to know about increasing, constant and decreasing returns to scale this would be expected at A level. For four marks you are expected to discuss how as the firm grows in the long run, it at first experiences increasing returns to scale between Q1 and Q3. This is because as it grows cost per unit falls and so it is able to produce more output per unit of input. At point Q3 the firm reaches the minimum efficient scale which is where cost per unit of output is at its lowest. Beyond Q3 decreasing returns to scale set in as cost per unit rises and the firms output per unit of input falls.
Hope this helps

Yes indeed