Concept:Units at hand = Opening stock + Purchases - Returns - Sales.Explanation:Treat the initial 100 units as opening stock.Net purchases = (200−80)+200+200=520 units.Total units available = 100+520=620 units.Total units sold = 160+180+120+100=560 units.Units at hand on July 30 = 620−560=60 units.Answer:60 units