SUMX

DenbyG , Create a measure like 

Calculate(sum(Fact[Value]), filter(Fact, Fact[Employer] in {"Employer 1","Employer 2","Employer 3"}))

or with joined dim 

Calculate(sum(Fact[Value]), filter(Dim, Dim[Employer] in {"Employer 1","Employer 2","Employer 3"}))

Need the same value in when use employeer in group by 

Calculate(sum(Fact[Value]),  Fact[Employer] in {"Employer 1","Employer 2","Employer 3"})

in needed refer: Difference in filtering data in CALCULATE with and without FILTER
https://youtu.be/KDcmzwgPvXQ

Hi DenbyG 

Total Funding for A, B, C =
CALCULATE(
    SUM(Employers[Total]),
    Employers[Employer] IN {"Employer A", "Employer B", "Employer C"}
)

SUM(Employers[Total]) adds up the values in the Total column.
CALCULATE changes the filter context so it only includes rows where Employer is one of the three specified.
The IN operator makes it easy to check multiple values.

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Hi DenbyG ,

try measure below:

Total Funding Selected Employers = 
CALCULATE(
    SUM('Employers'[Funding]),
    FILTER(
        'Employers',
        'Employers'[Employer Name] = "Employer A" ||
        'Employers'[Employer Name] = "Employer B" ||
        'Employers'[Employer Name] = "Employer C"
    )
)

Please give kudos or mark it as solution once confirmed.

Thanks and Regards,

Praful

DenbyG 

TotalFunding_ABC =
CALCULATE(
SUM('Employers'[Total]),
'Employers'[Employer] IN {"Employer A", "Employer B", "Employer C"}
)

If this answer helped, please click Kudos or Accept as Solution.
-Kedar
LinkedIn: https://www.linkedin.com/in/kedar-pande