Jamar owns a clothing store. His fixed costs are $⁢800 per month, and it costs $⁢10 to produce each item. Your revenue is $⁢0 when 0 items are sold and $⁢0 when 150 items are sold due to market saturation. The maximum revenue occurs when 75 items are sold. Write a system of equations for the linear cost function, C⁡(x) , and a quadratic revenue function, R⁡(x) , where x represents the number of items sold.