What is the average 2400 kwh/kw p y with a 1400 kwh/kw p y greater than 12.9, a 1200 kwh/kw p y greater than 21.7, and a 1600 kwh/kw p y greater than 18.8?
CREATE TABLE "cost_per_kilowatt_hour_us_cents_k_wh" (
  "20_years" text,
  "2400_k_wh_k_w_p_y" real,
  "2200_k_wh_k_w_p_y" real,
  "2000_k_wh_k_w_p_y" real,
  "1800_k_wh_k_w_p_y" real,
  "1600_k_wh_k_w_p_y" real,
  "1400_k_wh_k_w_p_y" real,
  "1200_k_wh_k_w_p_y" real,
  "1000_k_wh_k_w_p_y" real,
  "800_k_wh_k_w_p_y" real
);
SELECT AVG("2400_k_wh_k_w_p_y") FROM "cost_per_kilowatt_hour_us_cents_k_wh" WHERE "1400_k_wh_k_w_p_y">12.9 AND "1200_k_wh_k_w_p_y">21.7 AND "1600_k_wh_k_w_p_y">18.8;