Explanation:
The internal angles of a n-gon sum to ( n-2)(180)°
for this quadrilateral : ( 4-2)(180) = 360°
A + B + C + D = 360
105° + 105 + 90 + x = 360 ° ( I think B = 105 degrees....hard to see)
x = 60°
Maybe this is a kite
A = 90 B = 105 C = 90 then x = 75°