Modelling Algebraic expressions can be done through Algebra Tiles, this is done through squares and rectangles both representing variables and numbers. 4+8x and 4(2x+1) is equivalent because of its distributive property, in the second equation 4 is distributed or multiplied to 2x+1 making it 8x+4. To represent this with Algebra tiles, you need to divide the paper into two, draw a vertical line in the middle that represents equal sign and on the first column, you need to draw 4 squares and beside it are 8 thin rectangles and on the second column you need to draw 8 thin rectangles and beside it are 4 squares. If you can picture it out, basically both equations are equivalent.