[tex]14^{-x+10}~~ = ~~13^{3x} \\\\[-0.35em] ~\dotfill\\\\ \log(14^{10-x})=\log(13^{3x})\implies (10-x)\log(14)=x\log(13^3) \\\\\\ 10-x=\cfrac{x\log(13^3)}{\log(14)}\implies \cfrac{10-x}{x}=\cfrac{\log(13^3)}{\log(14)}\implies \cfrac{10}{x}-\cfrac{x}{x}=\cfrac{\log(13^3)}{\log(14)}[/tex]
[tex]\cfrac{10}{x}-1=\cfrac{\log(13^3)}{\log(14)}\implies \cfrac{10}{x}=\cfrac{\log(13^3)}{\log(14)}+1\implies \cfrac{10}{~~\frac{\log(13^3)}{\log(14)}+1~~}=x \\\\\\ \cfrac{10}{~~\frac{\log(13^3)+\log(14)}{\log(14)}~~}=x\implies \cfrac{10\log(14)}{\log(13^3)+\log(14)}=x[/tex]
