Answer: $54,000 per production run
Explanation:
As we are dealing with the decision of whether or not to process the good further, the irrelevant cost would be the cost of producing product B from input R.
This is because this cost has already been incurred to produce product B and so is a sunk cost. Sunk costs are irrelevant to the decision to process further.
30,000 units of B were made from 90,000 units R so the cost of B is:
= 30,000 / 50,000 * 90,000
= $54,000
The options here are probably for a variant of this question.