[latex]( \frac{6a+c}{ a^{2}-6ac }+ \frac{6a-c}{ a^{2}+6ac})* \frac{ a^{2}-36 c^{2} }{ a^{2}+ c^{2} } [/latex]

[latex]( \frac{6a+c}{ a^{2}-6ac }+ \frac{6a-c}{ a^{2}+6ac})* \frac{ a^{2}-36 c^{2} }{ a^{2}+ c^{2} } =( \frac{6a+c}{ a(a-6c) }+ \frac{6a-c}{ a(a+6c)})* \frac{ a^{2}-36 c^{2} }{ a^{2}+ c^{2} } =\\\\=\frac{12(a^2+c^2)}{a(a^2-36c^2)}*\frac{ a^{2}-36 c^{2} }{ a^{2}+ c^{2} }=\frac{12}{a}[/latex]