mini exercises – question 1

A butcher sells $300,000 of meat at a consistent mark up of 25%. His inventory at the start of the year was $15,000. This had increased by
20% by the end of the year.
Calculate the purchases for the year.

i did : sales 300,000
less cost of sales
opening inventory 15000
purchases x
less c/inventory (18000)
—————– (225,000)
————
Gross profit (markup 25%) 75,000

and finally i’m getting purchases amounted to : $ 228000

why is my answer wrong ?