question: What's the total number of NGC that has a Declination ( J2000 ) of °15′55″, and an Apparent magnitude greater than 10?
answer: SELECT SUM(ngc_number) FROM table_name_28 WHERE declination___j2000__ = "°15′55″" AND apparent_magnitude > 10
context: CREATE TABLE table_name_28 (ngc_number INTEGER, declination___j2000__ VARCHAR, apparent_magnitude VARCHAR)