Assume that for the month of September, a department has 26,000 equivalent units of materials and 81,000 equivalent units of conversion cost. For beginning work-in-process, the cost of materials is $24,000 and the conversion cost is $95,000. Costs added during September are $23,000 for materials and $154,000 for conversion. What is cost per unit for September? (Note: Round answer to three decimal places.)

a.$3.507 per unit b.$3.882 per unit c.$5.507 per unit d.$4.882 per unit

I know the answer is D. But could you please show which numbers to use? Any extra explanation is helpful. Thank you!