Does anyone know how to do this?
find the measure of ∠3?

72°

54°

36°

60°

The area of a triangle is 180° Each angle is 60° Angle 2 is half of 60° which is 30° so it's adjacent angle is also 30° A right angle is 90° So 90° + 30° = 120° Area of a triangle = 180° - 120° = angle 3 Angle 3 = 60°

60 degrees... Considering that this image is to scale and is a regular pentagon, because the dotted line is bisecting the 60 degrees.  Making the 60 degrees now thirty degrees, and now you know that the unlabeled angle is sixty because all degrees inside a triangle add up to 180.  Now remember how I said that the line was bisecting the angle before?  You can see that this is an isosceles triangle... (If you want I can prove that too XD)  Meaning that that bisector split the triangle into two congruent triangles... and CPCTC... or Corresponding Parts of Congruent Triangles are Congruent you know that y (that unnamed angle) are corresponding. So 3 is 60

21/2 or 5/2