$(14\%)$ Ouestion $3.$

The net energy of a bond is represented by the following expression:

$U-=\frac{-A}{r}+\frac{B}{9r^9},A=15{10}^{-20}Jnm,B=18\mathrm{.}8{10}^{-25}Jn{m}^9$

Where energy is expressed in joule $($N$.$m$)$ and r is interatomic distance in