Evaluate. Round your answer to the nearest thousandth.
log4 ^21

[tex]\log_4 21 = \dfrac{1}{2}\cdot \log_2 21 = \dfrac{1}{2}\cdot \left(\log_23+\log_2 7\right) \approx \dfrac{1}{2}\cdot\left(1.584+2.807\right) \approx 2.196[/tex]