For which set of data is the mean 8.1?
6.6, 7.5, 8.1, 9.2, 9.8
8.1, 8.1, 8.7, 8.8, 9.9
4.2, 6.7, 8.1, 5.5, 9.1
8.5, 8.0, 8.0, 9.0, 7.0

In the figure below, ∠dec ≅ ∠dce, ∠b ≅ ∠f, and segment df is congruent to segment bd. point c is the point of intersection between segment ag and segment bd, while point e is the point of intersection between segment ag and segment df. the figure shows a polygon comprised of three triangles, abc, dec, and gfe. prove δabc ≅ δgfe.