\[\boxed{\text{5.458.}}\]
\[3\frac{4}{9} = 2 + 1\frac{4}{9} = 2 + \frac{13}{9} = 2\frac{13}{9}\ \]
\[9\frac{21}{22} = 8 + 1\frac{21}{22} = 8 + \frac{43}{22} = 8\frac{43}{22}\ \]
\[4\frac{9}{10} = 3 + 1\frac{9}{10} = 3 + \frac{19}{10} = 3\frac{19}{10}\ \]