A part-whole model can be shown in different ways, but each of these models show two parts that add up to a whole. You can use addition to work out the whole number by adding the parts together.

Floyd R. Vest, A Catalog of Models for the Operations of Addition and Subtraction of Whole Numbers, Educational Studies in Mathematics, Vol. 2, No. 1 (Jul., 1969), pp. 59-68 ...