Which of the following could be used to calculate the measure of ∠ROP?
a.(6x − 4)° + (2x + 16)° = 180°
b.(x + 16)° + (6x − 4)° = 360°
c.(6x − 4)° + (2x + 16)° = 360°
d.(x + 16)° + (6x − 4)° = 180°