Please solve questions 11,13 and 15

Q11. If $$\begin{gathered} {\left(a^m\right)}^n=a^m.a^n, \mathrm{find} \mathrm{the} \mathrm{value} \mathrm{of}: \\ m\left(n-1\right)-\left(n-1\right) \end{gathered}$$
 

Dear student,
The solution to 11th question is given below.

Please post the other questions separately so that we can provide you with best answers.
Regards.