How to do comparing linear functions word problems

Please help to solve d

This value represents how much a change in one variable can be predicted from its relationship witha completely different variable .......

It costs a company $3,500 to produce 3,000 pencils whereas it costs the company $1,500a month even if they don't produce any pencils. If they sell the pencils for $0.75 and thecost, revenue, and profit functions are linear, determine how many pencils they must makein a month to break even