Hello there,
This is a regular polygon. To find the sum if its angle,
(n-2)180 (where n is the number of sides)
(4-2)180= 360 degrees
To find the unknown angle= 360-76-105-120
= 59
Angle x= 180 - 59 (angles on a straight line)
= 121 degrees
Hope this helps :))
~Top