CALCULATE

EVALUATE
  SUMMARIZECOLUMNS (
      'Sales'[Calendar Year],
      "All sales", SUM ( Sales[SalesAmount]),
      "Audio Sales", CALCULATE(SUM ( Sales[SalesAmount]), FILTER ( 'Sales', 'Sales'[ProductCategory] IN { "Audio" } )),
      "Computers Sales", CALCULATE(SUM ( Sales[SalesAmount]), FILTER ( 'Sales', 'Sales'[ProductCategory] IN { "Computers" } ))
  )

"results": [
    {
        "cols":[
            {
                "field":"Calendar Year",
                "dataType":"String"
            },
            {
                "field":"All sales",
                "dataType":"Double"
            },
            {
                "field":"Audio Sales",
                "dataType":"Double"
            },
            {
                "field":"Computers Sales",
                "dataType":"Double"
            }
        ],
        "values":[
            [
                "2011",
                3144079105,
                29715962,
                1146377582
            ],
            [
                "2012",
                2642196833,
                52913593,
                990107918
            ],
            [
                "2013",
                2554233583,
                68930677,
                1072722493
            ]
        ]
    }
]