Q # 1:)
I was absent from class I have missed my lacture of interpretation.
1:) Interpret the material , mix, yield variance
2:) Discuss the merits

Q # 2:)
3 factors to be considered in deciding whether a variance should be investigated

Please read the text book you have. I would suggest:
1. Management and Cost Accounting by Colin Drury
2. Standard Costing - CIMA publication