Difference equation (economic growth model)

$\displaystyle

\Delta A / A = B (aL)^\gamma A^\theta / A

$

$\displaystyle \Delta L / L = n$

$\displaystyle 0< \theta < 1$

$\displaystyle n, B , \gamma > 0$

I need to solve for the procentual growth in A in terms of the parameters. This should according to my textbook equal

$\displaystyle \Delta A / A = \gamma n / (1-\theta)$

I guess it IS NOT a constant but CONVERGES to the previous constant. The only thing is, I can't solve it, work it out properly...

Can anybody solve this for me or put me in the right direction ?

I hope this was placed in the right subforum. Difference equations aren't differential equations, but I don't know in what subfield of Math difference equations would fit. (I'm no math student)

This might also be pre university level math, I don't know. I have never studied difference equations in high school and took a fairly math intensive curriculum.

Many thanks in advance!