The candidates were required to compute the cost and revenue values for all the levels of output at a given unit price. They were expected to apply their understanding of the concepts of costs, revenue and market structures to answer the questions.
A greater proportion of candidates avoided the question. They found it difficult determining the total variable cost (TVC) and total cost (TC) values for each level of output. They also had difficulty identifying the market structure in which the firm is operating. The few candidates who attempted this question performed poorly.
There is the possibility that the poor performance level stems from the poor handling of the related topic by teachers.

The TVC is equal to the sum of marginal costs up to that level of output i.e
TVC0 = 0
TVC1 = 0 + 10 = $10
TVC2 = 0 + 10 + 20 = $30
TVC3 = 0 + 10 + 20 + 30 = $60
TVC4 = 0 + 10 + 20 + 30 +40 = $100
Total cost is the total variable cost plus the total fixed cost i.e.
TC0 = 0 + 20 = $20
TC1 = 10 + 20 = $30
TC2 = 30 + 20 = $50
TC3 = 60 + 20 = $80
TC4 = 100 + 20 = $120

Total Revenue for each level of output is obtained by multiplying output by unit price i.e.
0 * $30 = $0
1 * $30 = $30
2 * $30 = $60
3 * $30 = $90
4 * $30 = $120

The market structure in which the firm is operating is a perfect market. This is because the same price is charged in the market