How many 3 digit numbers contain at least one 7? With explanation please

The function c(x) = 400x – 0.2x2 represents the total costs for a company to produce a product, where c is the total cost in dollars and x is the number of units sold. which statement is true? one thousand units have the minimum cost of $200,000. one thousand units have the maximum cost of $200,000. two thousand units have the minimum cost of $800,000. two thousand units have the maximum cost of $800,000.