The $180k isn't NPV, unless you have a 0% discount rate. The payment schedule from the root comment was $500/month over 30 years, which comes to $6k/year. So this year you would have $14k more by accepting the $20k.

For the $20k lump sum to be worth the same as $6k/year for 30 years, you would need a rate of return of 43% (if my Excel-fu is correct). It would be better to take the $6k/year and take $20k as a cash advance on a credit card.

Sorry, I misinterpreted the meaning of the verb "worth" and worked backwards from what I assumed was the NPV. (and pulled a 20-yr term out of an orifice instead of the 30 years in TFA, whoops)