Please help!? Work out the size of angle x. 42 degrees and 123 degrees?

Answer:
Sorry I don´t know the answer but I tried
Step-by-step explanation:
Answer:
x° = 99°
Step-by-step explanation:
Sum of angles on a straight line is 180°.
Sum of angles in a triangle is 180°. Let u be the value of the unknown angle in the triangle.
u° = 180° - 57° - 42°
u° = 81°
Sum of angles on a straight line is 180°.
x° = 180° - 81°
x° = 99°