How much yield to expect?

[Ed B.]

I have  a chance to sell a  house and am comparing my options which are:

Keep the property for four years  and benefit from cash flow and potential appreciation, or

sell the property and invest the money in notes or other property to yield approximately the same  return I would have gotten by not selling. According to my rudimentary math, I would need to earn about 21%  compounded annually, to gain the same dollars by keeping.

My question:  How difficult would it be to find investments to earn 21%?

The easier option might be to try to sell the property for more. If I got 100K more on the selling price, I'd only have to earn about 10% on the sales proceeds to equal my gain of not selling.  

Thanks for any feedback/advice!