Expand and collect like terms:
[tex]\begin{gathered} =\text{ }7s^{\frac{7}{4}}\times t^{\frac{-5}{3}}\times-6s^{\frac{-11}{4}}\times t^{\frac{7}{3}} \\ =\text{ }7\times s^{\frac{7}{4}}\times-6\times s^{\frac{-11}{4}}\times t^{\frac{-5}{3}}\times t^{\frac{7}{3}} \\ =\text{ 7 }\times-6\text{ }\times\text{ }s^{\frac{7}{4}}\times s^{\frac{-11}{4}}\times t^{\frac{-5}{3}}\times t^{\frac{7}{3}} \\ =\text{ -42}\times\text{ }s^{\frac{7}{4}}\times s^{\frac{-11}{4}}\times t^{\frac{-5}{3}}\times t^{\frac{7}{3}} \end{gathered}[/tex]Bring the exponents having same base together:
[tex]\begin{gathered} \text{The multiplication betwe}en\text{ same base becomes addition } \\ \text{when the exponents are brought together} \\ =-42\text{ }\times\text{ }s^{\frac{7}{4}-\frac{11}{4}}\times t^{\frac{-5}{3}+\frac{7}{3}} \\ =\text{ -42 }\times s^{\frac{7-11}{4}}\times t^{\frac{-5+7}{3}} \\ =\text{ -42 }\times s^{\frac{-4}{4}}\times t^{\frac{2}{3}} \end{gathered}[/tex][tex]\begin{gathered} =\text{ -42 }\times s^{\frac{-4}{4}}\times t^{\frac{2}{3}} \\ =\text{ -42 }\times s^{-1}\times t^{\frac{2}{3}} \\ =\text{ -42}s^{-1}t^{\frac{2}{3}} \end{gathered}[/tex]