use this formula
[tex] log_{5}(10x + 5) - log_{5}(x - 7) = \\ log_{5}( \frac{10x + 5}{x - 7} ) [/tex]
after thet you have
[tex] log_{5}( \frac{10x + 5}{x - 7} ) = 2[/tex]
open this up
[tex] \frac{10x + 5}{x - 7} = {5}^{2} [/tex]
and from now you sould be fine!
