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

Multiple Choice

Solve the problem.
-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) $1 \mathrm {~m}$
B) $3 \mathrm {~m}$
C) $4 \mathrm {~m}$
D) $9 \mathrm {~m}$