Appendix B - Questions for Appendix B - Conversion of Units for Physical Quantities - Page A.22: 7a

$8.7 \times 10 ^{-18} m^2$

We convert to $m^2$. Remember that when there is a squared term or cubed term in the units, we need to adjust for that. For example, it we are converting from $mm^2$ to $m^2$, we need to multiply by $10^{-6},$ not $10^{-3}$. $8.7 \times 10 ^{-18} m^2$