Taxi or subway from Beijing Airport to days inn forbidden.

You can take the airport express train to Dongzhimen and transfer to line 2 to Jianguomen. Then take subway line 1 from Jianguomen to Tian'anmen East. Then get out of the station and walk along East Chang'an Street. Turn left at the crossing of Chang'an Street and Nanyanhe Street, and walk along Nanyanhe Street for about 200m, you will find the hotel.

As you'll arrive late at 8pm, I'd suggest you take a taxi to the hotel which may cost you about 15o yuan. If taking subway and transfer twice, you'll probably arrive at your hotel after 10pm.