The terms point, line and plane, are the undefined terms in geometry. They are so basic that these terms are used to define other terms in geometry. You can describe a point to be indicating a location or position without any thickness. A line is a series of points that travel in one direction infinitely at both ends. A plane is a flat surface of area. The diagram of line ST intersecting plane M at point R is shown in the attached picture.
A straight line has an angle of 180. A right angle has an angle of 90. Angle 3 is the same as angle 80°, 6, and 8. Angle 2 is the same as angle 4, 5, and 7. All you have to do is subtract the angle you know from 180, and what will be left off is Angle 3.
Then you find out what angles are the same and you have your answer.
Answer and work down below. Let me know if you have any questions