CREATE TABLE table_16634 ("School" TEXT, "Location" TEXT, "Enrolment" FLOAT, "Founded" FLOAT, "Denomination" TEXT, "Day/Boarding" TEXT, "School Colours" TEXT, "Abbreviation" TEXT, "In competition since" FLOAT)

What is the enrollment of STM which has been in competition since 1990?
SELECT COUNT("Enrolment") FROM table_16634 WHERE "In competition since" = '1990' AND "Abbreviation" = 'STM'
SELECT COUNT("Enrolment") FROM "table_16634" WHERE "Abbreviation" = 'STM' AND "In competition since" = '1990'