Custom M Script to sum values from Joined/Merged Queries

Here is what I would write in SQL to do the same....

select  t1.ID, t1.Capability.1, t1.Capability.2, t1.Capability.3
         ,t2.[Vehicle1Score] 
		 + case when t3.[Vehicle1Score] is null then 0 else t3.[Vehicle1Score] end
         + case when t4.[Vehicle1Score] is null then 0 else t4.[Vehicle1Score] end as [Vehicle1CapaScore]
      ,t2.[Vehicle2Score] 
		 + case when t3.[Vehicle2Score] is null then 0 else t3.[Vehicle2Score] end
         + case when t4.[Vehicle2Score] is null then 0 else t4.[Vehicle2Score] end as [Vehicle2CapaScore]
      ,t2.[Vehicle3Score] 
		 + case when t3.[Vehicle3Score] is null then 0 else t3.[Vehicle3Score] end
         + case when t4.[Vehicle3Score] is null then 0 else t4.[Vehicle3Score] end as [Vehicle3CapaScore]
from      Table1 as t1 left outer join
          Table2 as t2 on
          t1.Capability.1 = t2.[Capability] left outer join
          Table2 as t3 on
          t1.Capability.2 = t3.[Capability] left outer join
          Table2 as t4 on
          t1.Capability.3 = t4.[Capability] left outer join