I'm confused about how write linear equations to find the answers to the following:

Cost to make 3 items is $125, cost to make 7 is $125.

A. Assume liner relationship, determine rule for the cost C of making products s

Product sells for $25

B. Rule for the revenue R recieved from selling product s

C. Profit = revenue -cost. Rule for profit from selling products s. How many must be sold to break even

D. If she sells an average if t, Min price required to sell product s to breakeven. What if t =5

Any help or formulas would be greatly appreciated.

Thank-you