Measure (Multiply 2 columns from different tables) correct on lowest level but totals are too high

[JasiExpert]

I am a beginner, just had a 2 days training and started with my first projects. Now I am facing the following problem. I want to multiply 2 columns from 2 different tables.  The Measure "PlanBedarfStk" (#2 ist just another try) shows the correct value per item but the moment I select more than 1 item the totals are too high (calculation seems to happen on higher level). 

Table "PlanStkVK" (only relevant columns) 

ArtikelNr(itemNr)	Month	PlanStk (planned pcs)
abc-12345	2021/01	5
abc-12345	2021/02	0
abc-12355	2021/01	3

Table "vw_aevo_Stückliste_mPreis" shows all the elements required to produce the items 

ArtikelNr	ElementNr	Menge (pcs)	MEK (price)	MengexMek (calculated column)
abc-12345	bcd-12345	20	500	10.000
abc-12345	bxs-45623	25	10	250
abc-12355	xcv-56789	10	22	220

I guess the problem is the relation between the 2 tables (m:n).

Any ideas how i can solve this.

Finally I want to calculate the total costs of production (MengexMek) x (planned pieces).

But (Menge x planned pieces) already doesnt show correct figures if more than one item is selected.

Thanks a lot to the experts.

[JasiExpert]

Thank you soo much. 

[AlexisOlson · Accepted solution]

In general, (a + b + c) * (x + y + z) = a*x + a*y + a*z + b*x + b*y + b*z + c*x + c*y + c*z is not the same as a*x + b*y + c*z. I suspect you want the latter but your attempts are written like the former.

It's not completely clear to me how all your data tables are related so it's hard to say exactly, but you should be able to get the result you want using SUMX a bit like this:

_PlanBedarfStk =
SUMX ( VALUES ( vw_aevo[ArtikelNr] ), [_PlanStk] * [_MEKxStk] )