There are mathematical optimization calculations you could do, but at the end of the day, REI isn't an equation to solve.

It's Geometry that trains us how to multi-task.Algebra, is the study of how to execute the problems mathematically, and as long as the REI lives on the left side of the equal sign (the process), instead of the right (the end result), they will have control over the answer, and the strategies I spoke of above, can be found only on the left side of that equal sign.

The backstory about me: I'm a mathematics teacher in Denver and I love to see students have those AHA moments when they understand something.

It allows them to see the difference between the symptoms and the actual problems, and lay out a plan (financial) that works.The Algebra teaches how to analyze that problem, and work out the solution mathematically...with $$$ in front. 

Even when the market is high, it seems to still make sense to hold on to them, mathematically. 

I’m in agreement with most above, mathematics should always count more than psychology.

Mathematically speaking don't pay quarterly taxes if you don't have to, but be sure you have enough to pay your taxes when they come due.

I love learning and during my spare time, I am always reading books about personal development, software engineering, mathematics, physics, and being a successful introvert entrepreneur(Just call me Elon Musk Jr lol). 

Realize all of the above are not mathematical, so its your "assessment".Then, what's the answer.Lets say your future payoff is $200,000 in 15 years. 

A 9% cap = $577,777 (mathematically divide the NOI by .1 for 10% or .09 for 9%, etc).