An algebra tile configuration. Outside of the configuration are the following tiles: + x squared, + x, negative x, +, and negative. 0 tiles are in the Factor 1 spot and 0 tiles are in the Factor 2 spot. 9 tiles are in the Product spot in 5 columns with 5 rows. First row: 1 + x squared, 4 + x. Below the + x squared tile are 4 +x tiles.
What constant term is necessary to complete the perfect square trinomial pictured in the algebra tiles?

x2 + 8x +