Of the black officers, how many of them investigated cases between the years 2010 and 2015?
black refers to race = 'B'; between the years 2010 and 2015 refers to date between '2010-01-01' and '2015-12-31'; case refers to case_number
SELECT COUNT(T1.case_number) FROM officers AS T1 INNER JOIN incidents AS T2 ON T2.case_number = T1.case_number WHERE T1.race = 'B' AND T2.date BETWEEN '2010-01-01' AND '2015-12-31'