Answer: B
\(\sin(3x - 20^\circ) = \cos(3y + 20^\circ)\) i.e., \(\sin(3x - 20^\circ) = \sin[90^\circ - (3y + 20^\circ)]\) i.e., \(3x - 20^\circ = 90^\circ - (3y + 20^\circ)\) i.e., \(3x - 20^\circ = 90^\circ - 3y - 20^\circ\) i.e., \(3x + 3y = 90^\circ - 20^\circ + 20^\circ\) i.e., \(3(x + y) = 90^\circ\) i.e., \(x + y = 30^\circ\)
\(\sin(3x - 20^\circ) = \cos(3y + 20^\circ)\) i.e., \(\sin(3x - 20^\circ) = \sin[90^\circ - (3y + 20^\circ)]\) i.e., \(3x - 20^\circ = 90^\circ - (3y + 20^\circ)\) i.e., \(3x - 20^\circ = 90^\circ - 3y - 20^\circ\) i.e., \(3x + 3y = 90^\circ - 20^\circ + 20^\circ\) i.e., \(3(x + y) = 90^\circ\) i.e., \(x + y = 30^\circ\)