CREATE TABLE table_204_336 (id DECIMAL, "operators" TEXT, "named trains" TEXT, "destination" TEXT, "year begun" TEXT, "year discontinued" DECIMAL)

what is the difference -lrb- in years -rrb- between when the royal blue began and the year the crusader began ?
SELECT ABS((SELECT "year begun" FROM table_204_336 WHERE "named trains" = 'royal blue') - (SELECT "year begun" FROM table_204_336 WHERE "named trains" = 'crusader'))
SELECT ABS((SELECT "year begun" FROM "table_204_336" WHERE "named trains" = 'royal blue') - (SELECT "year begun" FROM "table_204_336" WHERE "named trains" = 'crusader'))