for this case we have that by definition, the sum of the internal angles of a traingule is 180 degrees.
In addition, the angle "R" of the triangle is given by:
[tex]R = 180-45x[/tex]
So, we have to:
[tex](180-45x) + 25x + (57 + x) = 180\\180-45x + 25x + 57 + x = 180\\-45x + 25x + 57 + x = 0\\-45x + 25x + x = -57\\-19x = -57\\x = \frac {57} {19}\\x = 3[/tex]
Answer:
[tex]x = 3[/tex]
