Okay, I think I understand.
Straight lines have a measure of 180°, so
52° + 59° + y = 180°
y = 69°
The measure of the inner angles of a polygon = (n - 2)180° where n is the number of sides. The shape is a triangle, so n = 3.
(3 - 2)180° = 63° + y + x
180° - 63° - (69°) = x
x = 48°