Check the picture below.
now, if the x-intercepts are at ±4 whilst the center is at the origin, that means the vertices are the ones hitting the x-axis, like in the picture, so just plug in the values for a, b, h and k.
now, if the x-intercepts are at ±4 whilst the center is at the origin, that means the vertices are the ones hitting the x-axis, like in the picture, so just plug in the values for a, b, h and k.