At a price of $20, the three firms in a market plan to supply 4, 7 and 10 units of a good. At a price of $25, they plan to supply 6, 9 and 13 units. Using these figures, explain how market supply is derived from the supply of individual firms and what the results show about the relationship between price and quantity supplied. The figures are invented.

Paper 2-style short part (standalone practice; not an IB question).