#Math Videos for kids #Learning videos for kids #math videos for 3rd grade #3rd grade #third grade #3rd grade math #common core math #learning video for kids #math videos for kids #elementary #grade 3 perimeter #math #perimeter and area #perimeter of a rectangle #teacher #how to find perimeter #math lessons #shapes #perimeter of a square #lessons homeschool #geometry #2d #3d #polygons #length #rectangles #squares