One of the dangers of radioactive fallout from a nuclear bomb is its 90Sr, which decays with a 29 year half-life. Because it has chemical properties much like those of calcium, the strontium, if ingested by a cow, becomes concentrated in the cow's milk. Some of the e0sr ends up in the bones of whoever drinks the milk. The energetic electrons emitted in the beta decay of 90Sr damage the bone marrow and thus impair the production of red blood cells. A 1 megaton bomb produces approximately 400 g of 90Sr. If the fallout spreads uniformly over a 2000 km2 area, what ground area would hold an amount of radioactivity equal to the "allowed" limit for one person, which ts 74000 counts/s?