REIT /RPAI - reverse split. I bought 1000 shares of REIT in 2004 for 10.000... they did a reverse split in 2012 (2.5 to 1) , I sold 200 in 2016, which cost basis should

In a 2.5 to 1 reverse split, your number shares is divided by 2.5 (1000 old shares became 400 new shares) and your cost basis is multiplied by 2.5 ($10 per old share became $25 per new share).

The cost basis for the 200 shares you sold is $25 x 200 = $5,000.