The problem is as follows:
1/4=64(1/4)^n-1
The answer is 5...
(I am working with Arithmetic Sequences.)
So you have the equation:
$\displaystyle \frac{1}{4}=64\cdot \left(\frac{1}{4}\right)^{n-1}$
Write the equation as:
$\displaystyle \frac{1}{4}=\left(\frac{1}{4}\right)^{-3}\cdot \left(\frac{1}{4}\right)^{n-1}$
$\displaystyle \Leftrightarrow \frac{1}{4}$ $\displaystyle = \left(\frac{1}{4}\right)^{n-4}$
...