That's $593M taxes on $1.34B earnings on exercising stock options...44% tax rate is pretty harsh!
Basically, you take revenue, divide it by the poverty level (he's got six kids, so around $45k - $50k), take the log base 10, and multiply by some constant that would be the same for everyone to match the government spending level - that constant these days is probably around 9 or 10. The result is your fair tax rate.