To start off with, DF=EG's reason is given, since you stated it was given.
Next, DE+EF = EF+FG's reason is because of the substitution property of equality. Think "if a = c, b = c, then a = b"
Lastly, DE = FG's reason is because of the Subtraction property of equality. If you subtract EF on one side, you must do it on the other side.
You FOIL (First, Outer, Inner, Last)
If you FOIL, you should get 2y^2 - 4y + 4y^2 - 8y +12y -24
180 degrees is half of a circle, and clockwise means turning in the direction a clock does - right.
So a point would be turned right halfway around.
Answer:
x^4 + 5x^3 - 12x^2 + 5x + 1