Answer
Simple Cubic = 1 atom
Body-centered = 2 atoms
Face-centered = 4 atoms
Work Step by Step
Simple cubic cells have one-eighth of a sphere inside the realm of the cell on each vertex, adding up to one whole atom.
Body-centered cubic cells have the fractions of spheres on each vertex also, but include one whole atom in the center, two atoms altogether.
Face-centered cubic cells have simple cubic cell's vertex spheres, but also have one-half of a sphere flushed on each face, totaling 4 spheres.