From the following data, find the $2019$ Net Sales index number, using $2015$ as the base year. $($Round to the nearest tenth percent.$)$

International Industries$5$ Year Selected Financial Data

$20192018201720162015$

Net Sales $491,290459,620488,960461,280431,400$

Net Income $42,47043,78047,59051,73051,730$

Total Assets $141,540148,990156,830156,830146,570$