This is a sudoku puzzle.
It is made up of a 4x4 picture grid.
Some of the pictures are already in place in the grid.
The others are in a pile to the left of the grid.
Your task is to input the missing pictures.
Each row and each column have the same pictures in them [add] [subtract] [multiply] [divide].
You can move the inputted pictures around within the frames at any time.
* Take care, when you add the last one the grid becomes "frozen".
To start the activity again simply refresh the page.