solution:
The first step is that both the top and bottom forces cancel out because if you remember that each atom has either a +e or -e, you can conclude that since they are at the same length, that they cancel.
So the only part you really need to worry about is the middle one with the distance of .300 nm. From there, you find the distance between both bonds of N-H (one is....11 while the other is .19).
Then for each one you use [tex]f=k\frac{e^2}{r^2.k}=9\times10^9\\[/tex]
[tex]e is 1.6\times10^{-9} and1.9\times10^{-8}\\[/tex]
If you calculate both correctly, you will get[tex]6.38\times10^{-9} and 1.9\times10{-8}\\[/tex]Then just add the two and you got the answer!
[tex]1.26\times10^{-8}[/tex]
