Doubt Regarding Updates in study material

Recently I was going through the prefix sums topic in silver and i really loved the material
and I also remember there was interesting problem in the bottom which was computation of
sums of this form 1a[i] +2a[i+1] + 3*a[i+2]+…
. I am unable to find it now so I think there must be an update and why its missing now?

It got removed since it isn’t really relevant to USACO.

It was moved into the solution for: