context: The median lethal dose (LD50) for acute radiation exposure is about 4.5 Sievert. The committed effective dose equivalent (CEDE) 210Po is 0.51 µSv/Becquerel if ingested, and 2.5 µSv/Bq if inhaled. So a fatal 4.5 Sv dose can be caused by ingesting , about 50 nanograms (ng), or inhaling , about 10 ng. One gram of 210Po could thus in theory poison 20 million people of whom 10 million would die. The actual toxicity of 210Po is lower than these estimates because radiation exposure that is spread out over several weeks (the biological half-life of polonium in humans is 30 to 50 days) is somewhat less damaging than an instantaneous dose. It has been estimated that a median lethal dose of 210Po is , or 0.089 micrograms, still an extremely small amount. For comparison, one grain of salt is about 0.06 mg  60 μg.
question: How many more nanograms is a fatal 4.5 Sv dose for ingesting than inhaling?
answer: 40