(12\cdot 5^{2n+1}-8\cdot 5^{2n}+4*5^{2n-1}):(4\cdot5^{2n-2})=
=(12\cdot5^{2n}\cdot 5-8\cdot5^{2n}+4*5^{2n}\cdot 5^{-1}):(4\cdot5^{2n}\cdot 5^{-2})=
=\frac{5^{2n}\cdot 60-8\cdot 5^{2n}+5^{2n}\cdot 4\cdot \frac{1}{5}}{5^{2n}\cdot 4\cdot (\frac{1}{5})^2}
=\frac{5^{2n}\cdot (60-8+\frac{4}{5})}{5^{2n}(4\cdot \frac{1}{25})}=
=\frac{\frac{300-40+4}{5}}{\frac{4}{25}}=
=\frac{\not264^{66}}{\not5^1}\cdot \frac{\not25^{5}}{\not4^1}=
=66\cdot 5=330