Given that ∠xqr = 180° and ∠lqm = 180°, which equation could be used to solve problems involving the relationships between ∠mqr and ∠lqr?
a) (3a + 50) + 180 = (140 − 4a)
b) (3a + 50) + (140 − 4a) = 180
c) (140 − 4a) − 180 = (3a + 50)
d) (3a + 50) − (140 − 4a) = 180