Hello Tayba,
Beginning Inventory + Purchases = Ending Invenory+ Cost of goods sold
Gross margin is 20%, so Cost of goods sold equals 80% of sales (200,000 * 80%)=160,000
Beginning Inventory for the quarter is 30,000$
Purchases for the Quarter is 190,000$
Now you can replace those amounts in the equation to get the Ending Inventory as of 31 March
Ending Inventory as of 31 March=30,000+190,000-160,000
=60,000$