Table:
text: PRR locomotive classification
Baldwin Locomotive Works
Baldwin Locomotive Works
PRR_Class Builder_s_Model Build_date Total_produced Wheel_arrangement Service Power_output
BS6 VO-660 1942–1945 12 B-B Switcher hp (kW)
BS6 DS-4-4-660 1942–1945 99 B-B Switcher hp (kW)
BS7 DS-4-4-750 1951 24 B-B Switcher hp (kW)
BS7 S7 1951 7 B-B Switcher hp (kW)
BS10 VO 1943–1945 8 B-B Switcher hp (kW)
BS10 DS-4-4-1000 1948–1950 137 B-B Switcher hp (kW)
BS12 S-12 1951–1956 98 B-B Switcher hp (kW)
BF15 DR-4-4-1500 1940–1950 34 B-B Freight hp (kW)
BF16 RF-16 (A) 1950–1952 72 B-B Freight hp (kW)
BF16 RF-16 (B) 1950–1952 30 B-B Freight hp (kW)
BP60a DR-12-8-3000 1947–1948 24 2-D-D-2 Pass hp (kW)
BP20 DR-6-4-2000 1948 18 A1A-A1A Pass hp (kW)

text: PRR locomotive classification
Baldwin Locomotive Works
Baldwin Locomotive Works
PRR_Class Builder_s_Model Build_date Total_produced Wheel_arrangement Service Power_output
BP20 DR-6-4-2000 1948 9 A1A-A1A Pass hp (kW)
BRS10 DRS-4-4-1000 1949–1950 6 B-B Pass hp (kW)
BRS12 RS-12 1951–1954 8 B-B Pass hp (kW)
BRS15 DRS-4-4-1500 1950 8 B-B Pass hp (kW)
BRS16 AS-16 1953–1955 28 C-C Pass hp (kW)
BRS24 RT-624 1951–1954 22 C-C Transfer hp (kW)
LRS25 T2500 1950–1951 22 C-C Transfer hp (kW)

Question: How many units were built in total of model ds-4-4-660 with a bb wheel arrangement and a PRR class of bs6 under the Baldwin Locomotive Works classification?