StubHub 1099-K Sold Concert Tickets

I received a 1099-K from StubHub.  I see in TurboTax where I can enter the 1099-k and I select sale of personal items. 

I am then able to enter the amount from box 1a.

 

My issue is that I sold these tickets for a small profit. I don’t see any place to enter the purchase price of the tickets.

 

Do I just subtract this from my box 1a amount and enter that value? I am struggling to find where I can enter the cost of the tickets so I am only taxed in the investment gain and not the full amount from the 1099-k.

 

thanks