CREATE TABLE table_20186 ("Class" TEXT, "Wheel Arrangement" TEXT, "Railway" TEXT, "Number at Doncaster" FLOAT, "Number at Pyewipe" FLOAT, "Number at March" FLOAT)

Name the number at march when class is j66
SELECT "Number at March" FROM table_20186 WHERE "Class" = 'J66'
SELECT "Number at March" FROM "table_20186" WHERE "Class" = 'J66'