It's not just that your math is ridiculous (as you acknowledge), it doesn't make any sense.
Greenland has almost no economy, a mere $2.7b in GDP, and few assets. You can't use negative $22 trillion as the basis with the US while ignoring the $110 trillion in household wealth and massive corporate & government assets (stacked against $50t-$55t in total debt between household + corporate + government). That's the part that makes no sense.
The asset value of everything in the US is at least $150t in the positive after you remove all debt. That's while ignoring additional value that should be applied to the annual output of the economic activity - and considerations for future gains - within the US territory and any other fringe benefits that go with it all as a package deal (USD global reserve currency, US military, 50 top universities, etc).
Greenland has 56,000 people producing a GDP per capita of $48,000. The US has 330 million people producing a GDP per capita of ~$63,500 or so (about 119% higher than Europe's $29,000 per capita). You get the people with the territory in the US, and they're among the most productive on earth in terms of per capita output.
A better number would be $65,000+ per acre before you include consideration for annual output and other benefits. If you count everything, it'd be far over $100,000 per acre.