Answer:
Production= 24,000 units 
Step-by-step explanation:
Giving the following information: 
Desired ending inventory= 20% of next month's sales
Sales:
August= 30,000
September= 20,000
October= 40,000
To calculate the production for September, we need to use the following formula:
Production= sales + desired ending inventory - beginning inventory
Production= 20,000 + 40,000*0.2 - 20,000*0.2
Production= 24,000 units