Two population function can be cleared up if money is spent on them according to the functions Z₁= 780 - 12c₁^0.5 and Z₂ = 600 - 8c₂^0.5 where Z₁ and Z₂ are the pollution levels from the two sources and C₁ and C₂ are expenditures levels (000s) on pollution reduction. What is the cheapest way of reducing the total pollution level from 1,380, which is the level it would be without any controls, to 1,000?