This is not possible, you have 2 variables in the expression - K and X, you can plot for one X value only if the K differs, but it doesn't matter, the plot will look the same regardless of X value, because the ∑(K*X) can be rewritten as X*∑(K)

You have 2 ways how to do it, unforunately with some manual effort

1. by using a list

2. by using a spreadsheet

ad1)

let's assume you want to plot K from 1 to 25 with step 1 for X=1

in Run-Mat

Seq(K,K,1,25,1) ->List 1

Cuml List 1->List 2

go to Stat module

and press F1 (grph) and press F1 (gph1) and your plot is ready, you can select from 3 gph only (gph1, gph2 and gph3)

for different X you need to add other calculation before going to stat module

5*List 2->List 3

ad2)

fill the seq in column A

fill the summation formula in column B

create the plot