CREATE TABLE table_75395 ("Years tallest" TEXT, "Name" TEXT, "Height ft / m" TEXT, "Floors" FLOAT, "Year completed" FLOAT)

What year was the building completed that has 10 floors?
SELECT AVG("Year completed") FROM table_75395 WHERE "Floors" = '10'
SELECT AVG("Year completed") FROM "table_75395" WHERE "Floors" = '10'