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