Match & Sum values from another table?

Hi! Your first table, the one with name and line number (line number being unique) is your dimension table. Your second table (the one with multiple rows with the same line number) is your fact table. Create a join between the two tables. In the model tab, you should see a line go from dim to fact and see a 1 by the dim table, a * by the fact table (indicating a 1 to M  join) and an arrow pointing at the fact table (which signifies that the dim table will filter the fact table. Next, create a measure for the length like this Length = SUM('YourFactTableName'[Length]). Add a table visual (or whatever viz you want) and put in the line number from your dim table and the measure you created.