The tangent and normal to the curve $\displaystyle y=4\sqrt{x+2}$ at the point P(7,12) cut the x-axis at points M and N respectively. Calculate the area of the triangle PMN.

My attempt is...

$\displaystyle \frac{dy}{dx}=\frac{2}{\sqrt{x+2}}$

Tangent : $\displaystyle y-12=\frac{2(x-7)}{\sqrt{x+2}}$

I guess I need some help in solving for x...