10000000 MINT X 0.2 = 2000000 MINT and...
365 days in a year divided by 20 yields 18.25 minting periods so...
2000000 MINT / 18.25 minting periods = 109589.041 MINT per minting period, this will equal 20% annual return from 10M MINT.
Of course that doesn't account for compound interest. You could apply a compounding interest calculator to figure it though.