You didn't actually answer my question about the meaning of the notation, but the answers are consistent with my guess that the first number is the base. So in the notation I am familiar with, the problem is:
If [MATH]\log_{3-\sqrt{7}}32 = a[/MATH], then find [MATH]\log_8(3+\sqrt{7})[/MATH],
where the subscripts are the bases.
As I suggested, I would express the given log in terms of base 2, and solve for [MATH]\log_2(3-\sqrt{7})[/MATH]. Do you know the change of base, formula, [MATH]\log_a x = \frac{\log_b x}{\log_b a}[/MATH] ? (In your notation, [MATH]^a\log x = \frac{^b\log x}{^b\log a}[/MATH])
Also, one way to deal with the conjugates [MATH]3-\sqrt{7}[/MATH] and [MATH]3+\sqrt{7}[/MATH] is to note that their product is 2, so [MATH]3+\sqrt{7} = \frac{2}{ 3-\sqrt{7}}[/MATH].
Please show what you can do, so we can help you wherever you are having trouble.
It
is fun!