CREATE TABLE table_15318324_1 (r_z___arcsecond__ VARCHAR, r_y___arcsecond__ VARCHAR)

How many values of r z (arcsecond) correspond with a r y (arcsecond) value of 0.247?
SELECT r_z___arcsecond__ FROM table_15318324_1 WHERE r_y___arcsecond__ = "−0.247"
SELECT "r_z___arcsecond__" FROM "table_15318324_1" WHERE "r_y___arcsecond__" = "−0.247"