CREATE TABLE table_62928 ("Campus" TEXT, "Year opened" TEXT, "Students" TEXT, "Size" TEXT, "Location" TEXT)

What year was the school opened that has a size of 10 acres and students of na?
SELECT "Year opened" FROM table_62928 WHERE "Students" = 'na' AND "Size" = '10 acres'
SELECT "Year opened" FROM "table_62928" WHERE "Size" = '10 acres' AND "Students" = 'na'