Most important for me is the result as I made this exercise and my result is different as given in the book.
I have a somewhat intricate solution.
. . Maybe someone can do better . . .
I converted the terms to the same base.
. . Take logs: .
. . Hence: . .
From the Base-Change Formula: . .
Substitute  and  into : .
We have: .
Muliply by . . . assuming
Multiply by 2: .
There are two cases:
Then we have: .