Solve the Problem $9 \mathrm {~m}$ Deep And $12 \mathrm {~m}$ Wide, How Far Is the Focus from the Vertex?
A)

Multiple Choice

Solve the problem.
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A radio telescope has a parabolic surface. If it is $9 \mathrm {~m}$ deep and $12 \mathrm {~m}$ wide, how far is the focus from the vertex?

A) $4 \mathrm {~m}$
B) $3 \mathrm {~m}$
C) $1 \mathrm {~m}$
D) $9 \mathrm {~m}$