An algebra tile configuration. Only the Product spot is shown. 8 tiles are in the Product spot in 3 columns with 3 rows. First row: 1 + x squared, 2 + x. Second row: 1 +x, 2 +. Third row: 1 +x, 1 +.
How many more unit tiles need to be added to the expression x2+4x+3 in order to form a perfect square trinomial?

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