what is the under or overstatement in COGS in 2019?

Acme Co. uses a periodic inventory system. Beginning inventory on January 1, 2019, was understated by $30,000, and ending inventory on December 31, 2019, was understated by $17,000. In addition, purchases of merchandise during 2019 was understated by $18,000. If none of these errors were discovered until after the 2019 books were closed, what was the under or over-statement in cost of goods sold in 2019? (If over-stated, enter a positive number; if under-stated, enter a negative number.)