a) $(\frac{1}{3})^{m}$ = $\frac{1}{81}$ $\Rightarrow$ $(\frac{1}{3})^{m}$ = $\frac{1}{3^{4}}$ $\Rightarrow$ $(\frac{1}{3})^{m}$ = $(\frac{1}{3})^{4}$ $\Rightarrow$ m = 4;

b) $(\frac{3}{5})^{n}$ = $(\frac{9}{25})^{5}$ $\Rightarrow$ $(\frac{3}{5})^{n}$ = $[(\frac{3}{5})^{2}]^{5}$ $\Rightarrow$ $(\frac{3}{5})^{n}$ =  $(\frac{3}{5})^{10}$ $\Rightarrow$ n = 10;              

c) (-0,25)$^{p}$ = $\frac{1}{256}$ $\Rightarrow$ $(\frac{-1}{4})^{p}$ = $(\frac{1}{4})^{8}$ $\Rightarrow$ p = 8.