Beams of Light Parallel to the Axis of the Parabolic

Multiple Choice

Beams of light parallel to the axis of the parabolic mirror shown in the figure strike the mirror and are reflected. Find the distance from the vertex to the point where the beams concentrate. ​
A = 12 ft, b = 8 ft
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A) The focus is 32 in. from the vertex on the axis of the parabola.
B) The focus is 16 in. from the vertex on the axis of the parabola.
C) The focus is 12 in. from the vertex on the axis of the parabola.
D) The focus is 8 in. from the vertex on the axis of the parabola.