For Amazon.com's device with a weight of 221g (7.8oz) how many screen pixels does the device have?
CREATE TABLE "electronic_paper_displays" (
  "maker" text,
  "model" text,
  "intro_year" text,
  "screen_size_inch" text,
  "self_lit" text,
  "screen_type" text,
  "weight" text,
  "screen_pixels" text,
  "touch_screen" text,
  "micro_sdhc" text
);
SELECT "screen_pixels" FROM "electronic_paper_displays" WHERE "maker"='amazon.com' AND "weight"='221g (7.8oz)';