notice that there is a triangle formed on the left of the drawing. It has two angles whose measure is known: 60 degrees and 55 degrees. The third angle is not identified with its measure, but we can easily find what the value is, because there is a very fundamental theorem of triangles that tells us that the ADDITION of ALL internal angles of a triangle must give 180 degrees.
Then, we can find the measure of the third angle by creating a very simple formula using the letter "x" to represent our unknown angle, and then solving for it.
The addition of all three angles in our triangle must equal 180.
we express those words in matematical form like this:
60 degrees + 55 degrees + x = 180 degrees
or to be a little simpler:
60 + 55 + x = 180
we combine the two numbers on the left of our equation:
115 + x = 180 subtract 115 from both sides:
x =