Fetch data from RelatedTable and Selected Column

I have 4 tables linked as follows:

• Tab_sales and tab_Entity: 1 to many relationship (one side from tab_Entity) using column Entity
• Tab_Entity and Tab_forex: a many-to-many relationship using column CURRENCY
• Tab_forex and Tab_scenario: 1 to many relationship (one side from tab_scenario) using column Scenario
• Tab_scenario_forex: 1 to many relationship (1 side from tab_scenarioForex) using column Scenario

I'd like to create a calculated column in Tab_Entity fetching the value Ex. rate from tab_Forex, changing based on the value selected from tab_scenario, so that I can choose the exchange rate I want to use for Sales (either ACT or Plan).

I tried this way creating a calculated column in tab_Entity:

forex = CALCULATE (SUMX('Tab_forex', 'Tab_forex'[Ex rate]),

RELATEDTABLE(Tab_Forex)

but the results is not filtered by Scenario from tab_Scenario_forex

Anybody can recommend a solution?

Thanks a lot

Mark

Tab_sales

Tab_Entity

Tab_forex

Tab_Scenario_Forex