\[\left( 1\frac{1}{2}a^{26}b^{14} \right)^{3} = \left( \frac{3}{2} \right)^{3}a^{78}b^{42} =\]
\[= \frac{27}{8}a^{78}b^{42} = 3\frac{3}{8}a^{78}b^{42}\]