The question is:

Find x, such that the slope of the tangent to the curve $\displaystyle y=tanx$ is equal to 4. (over $\displaystyle [0,2\pi)$)

I've got:

$\displaystyle \frac{d}{dx}tanx=sec^2x$

I think I should set that equal to 4, but I'm not sure on how I'm supposed solve it. Any help would be appreciated.