The area of a circle is pi times the radius of the circle squared. The radius of a circle is half the length of the diameter, so you can divide 2x+4 by 2 to get the radius, which would be x+2. Then, you plug it into the formula to get pi times (x+2)^2. You can FOIL that out to get x^2 + 4x + 4 and multiply that by pi, or you can leave it as it was before FOILing.
