Answer
a) $1.0552\times10^{-22}\ g$
b) $\$6.3\times10^{-22}/atom$
Work Step by Step
Atomic weight of copper: $63.546\ g/mol$
a) $63.546\ g/mol \div (6.022\times10^{23}\ atoms/mol)=1.0552\times10^{-22}\ g$
b) Number of atoms in the wire:
$7.0\ g\ wire \times \frac{99.999}{100}g\ Cu/g\ wire \div (1.0552\times10^{-22}\ g\ Cu/atom) = 6.6\times10^{22} atoms$
Price per atom:
$\$41.70\div(6.6\times10^{22} atoms) = \$6.3\times10^{-22}/atom$
