from Master's Theorem we get: T(n) = O($n^{\log_{4}5}$)
Now:$\log_{4}5 = \frac{\log_{2} 5}{\log_{2} 4} = \frac{\log_{2} 5}{2\log_{2} 2} = \frac{1}{2}\times \frac{\log_{2} 5}{\log_{2} 2} = \frac{\log_{2} 5^{1/2}}{\log_{2} 2} = \frac{\log_{2} 5^{1/2}}{1} = \log 5^{1/2}$
T(n) = O($n^{\log5^{1/2}}$)
Answer should be B