center at (2,4), focus at (7,4), contains point (5,8)
$\displaystyle \frac{(x-2)^2}{a^2} + \frac{(y-4)^2}{b^2} = 1$
$\displaystyle c = 5$
since the focal length is in the y-direction ...
$\displaystyle b^2 = a^2 + c^2$
substitute the given coordinates for $\displaystyle x$ and $\displaystyle y$ and solve for $\displaystyle a^2$ and $\displaystyle b^2$