Answer:
57
Step-by-step explanation:
All angles, no matter the shape, must add up to 360 degrees.
So simply add what you have, and then subtract from 360 to find missing piece.
121 + 108 + 82= 308.
365-308= 57.
Total sum of angles in a quadrilateral is equal to 360°.
therefore,
121°+105°+82°+a= 360°
308°+a=360°
a=360°-308°
a=52°
