CREATE TABLE table_24836 ("Episode number" FLOAT, "Title" CLOB, "Original airing on Channel 4" CLOB, "Time of airing on Channel 4" CLOB, "Original airing on E4" CLOB, "Time of airing on E4" CLOB, "Position in Channel 4s ratings a" CLOB, "Position in E4s ratings b" CLOB, "Total viewers" CLOB)

How many total viewers have April 21, 2010 as the original airing on channel 4?
SELECT COUNT("Total viewers") FROM table_24836 WHERE "Original airing on Channel 4" = 'April 21, 2010'
SELECT COUNT("Total viewers") FROM "table_24836" WHERE "Original airing on Channel 4" = 'April 21, 2010'