Alex is trying to fix his car by buying new parts. Alex needs to buy the following: Brakes ($850)
Wipers ($25)
Tires ($400)
Spark Plug ($75)
He mows yards for people in the neighborhood in order to cover the cost of his car parts. His charging price per yard is always the same. He has determined that he must mow 45 yards to cover the cost of his car parts.

PART A. Build a function that can be used to find the total profit, f(x), Alex earns by mowing x yards. Show your work to build this function.

PART B. Alex wants to make at least $500 more than what he spends on car parts. What is the minimum number of yards that must be mowed in order for Alex to reach his goal? Use mathematics to justify your response.