equation solving – Problems with the “Do” function?

Good morning,
I’ve been trying to solve this exercise for a couple days. At first, I don’t see any possible code errors.
But when I apply the “Do” function, to get the numerical value, it still gives the equation.

I attach images to show it.
enter image description here

As you can see, only the first 3 equations are solved.
The mathematica file is: https://www.wolframcloud.com/obj/0de92181-6864-4c54-90c2-04cfb674b608

Thank you very much for your help!