If the interest rate is $ r $, it follows that $$20000(1+r)^2 + 20000(1+r) + 20000 \ge 66200.$$ If we set $ x = 1+r $ and divide through the inequality by $ 200 $, it follows that $$100x^2 + 100x - 231 \ge 0.$$ Since $ 231 = 11 \cdot 21 $, we can factor the quadratic as $ (10x - 11)(10x + 21) \ge 0 $, so it follows that $ x \ge \frac {11}{10} $ or $ x \le \frac{-21}{10} $. Since we are looking for an interest rate percentage, it follows that $ x \ge \frac{11}{10} = 1.1 $, and $ r = x - 1 = \boxed{10}\% $.