tolong bantu soala nya susah

[tex]a. \: 4x + {90}^{0} + 2x = 180^{0} \\ 6x = 180^{0} - 90^{0} \\ 6x = 90^{0} \\ x = (\frac{90}{6} )^{0}[/tex]
b. sudut BOC = 90°
c. sudut AOB = 4x = 4 × 15° = 60°
d. sudut COD = 2x = 2 × 15° = 30°