that you are not asked for the total costs if the firm makes and the total costs if the firm buys, but instead for the difference between these two total cost numbers. Make sure that you read the question carefully so that you can attach the correct sign (+ or -) to your numerical answer. Oxford Engineering manufactures small engines. The engines are sold to manufacturers who install them in such products as lawn mowers. The company currently manufactures all the parts used in these engines, but it is considering a proposal from Tidnish Electronics, a reliable supplier, to supply starter assembly units for $6.50 each. The starter assembly is currently manufactured in Division 3 of Oxford Engineering. Last year, Division 3 manufactured 158,000 starter assemblies, but over the next several years, it is expected that 194,000 assemblies will be needed each year. Total costs related to the starter assembly for last year were as follows: Direct material $385,520 Direct labor $180,120 Total overhead $474,000 Total $1,039,640 Further analysis of overhead revealed the following information: $260,700 of total overhead was fixed. $147,700 of the fixed overhead can be avoided if the starter assembly is purchased from the supplier. Also, if the company buys the assembly from Tidnish, sales of another product can be increased, resulting in additional contribution margin of $36,000 with no additional fixed costs