The first week daily rankings are all in top 3:
08/04/30(水) MilkyWay「アナタボシ」
*3 *3 *2 *3 *3 *3 *3
So we have index numbers for every day:
04/28 1,144
04/29 3,788
04/30 3,987
05/01 1,815
05/02 1,217
05/03 2,004
05/04 1,651
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Total: 15,606
Predicted sales for the first week: 1.80 * 15,606 = ~28K