These two waves travel along the same string: y1(x, t) = (4.60 mm) sin (2x 400t)

These two waves travel along the same string: y1(x, t) = (4.60 mm) sin (2πx – 400πt) y2(x, t) = (5.60 mm) sin (2πx – 400πt + 0.80π rad). What are?
(a) The amplitude and
(b) The phase angle (relative to wave 1) of the resultant wave?
(c) If a third wave of amplitude 5.00 mm is also to be sent along the string in the same direction as the flrst two waves, what should be its phase angle in order to maxrmrzethe amplitude of the new resultant wave?