Can you help me step by step please?

Q.3) Suppose that a firm is planning to decontaminate two pollution sources in the city. Two pollution sources can be cleaned up if money is spent on them according to the functions 21 = 780 12C2'5 22 = 600 862'5 where 21 and Z 2 are pollution levels and C1 and C 2 are expenditure levels (in TLOOOS) on reducing pollution. What is the cheapest way of reducing the total pollution level to 1,380