i need to determine the surface area of the portion of the sphere $\displaystyle x^2 + y^2 + z^2 = 16$ that lies between the planes $\displaystyle z=1$ and $\displaystyle z=2$

i have taken the derivatives with respect to x and y and have switched to polar coordinates and now i have the integral:

$\displaystyle \int \int {{(4/\sqrt(16-r^2)dA}}$

I am not sure what the limits of the integrals will be. But i am pretty sure the leftmost integral has the limits 0 to $\displaystyle 2\pi$. can someone help me figure out the limits of the integrals? thanks.