As you can see there is a 4x4 grid.
Some of the numbers are in place but some are missing.
Those are in the pile of numbers to the left.
The numbers at the end of each row and at the bottom of each column are the totals of that row or column.
Drag 4 of the 5 numbers from the pile into the spaces in the grid.
Move them around to make the totals.
*Take care, when the last number is added the grid becomes "frozen".
To restart the activity just refresh the page.