The "standard form" for an ellipse is
[tex]\frac{(x- x_0)^2}{a^2}+ \frac{(y- y_0)^2}{b^2}= 1[/tex]
Where [itex](x_0,y_0)[/itex] is the center of the ellipse, a is the distance from the center of the ellipse and points where the ellipse crosses the x-axis and b is the distance from the center of the ellipse to the points where the ellipse crosses the y- axis. First change your equation to that form (Notice the "1" on the right hand side. How do you get that?). What does that tell you about the total width of the ellipse?