How many clients who were born in 1920 stay in east Bohemia?
East Bohemia appears in the column A3, which refers to the region.
SELECT COUNT(T1.client_id) FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id WHERE STRFTIME('%Y', T1.birth_date) = '1920' AND T2.A3 = 'east Bohemia'