Richardson & Sons purchased direct material worth $15 000 during the most recent period. At the end of the period the direct material account balance was $6 000 larger than the beginning balance. Cost of goods sold was $150 000. Overhead is applied at 50 per cent of direct labour cost. Other account balances are: Beginning Ending Work in process $75 000 $20 000 Finished goods $110 000 $60 000 What is the amount of prime cost added to production for the period