So, looking at some good examples from Annie, seven lots of g is the same length as seven lots of r plus seven lots of w. Or in letters:
7g = 7r + 7w
The two lines are the same length, so the two rows of rods are equal.
We made our own pairs of lines of rods.
Later on 4G tried a pair of squares like this.
4B built on top of theirs like this.
And we even tried cubes!
Here is James P's cube and the algebra to go with it:
Have a look at a slideshow of our work.