Spartan castings must implement a manufacturing process that reduces the amount of paritculates emitted into the atmosphere. two processes have been identified that provide the same level of particulate reduction. the first process is expected to incur $350,000 of fixed costs per year and add $50 of variable costs to east casting spartan produces. the second process has fixed costs of $150,000 per year and adds $90 of variable cost per casting. a. what is the point of indifference? b. if the expected number of castings is 4000, which process should be purchased? explain your answer.