According to the sine theorem: (a+b)/(Sina+sinb) = c/sinc, substitute the data to get Sina+sinb = (3 √ 2+√ 6)/4, Sina+sin (120-a) = (3 √ 2+√ 6). We get: (√ 3/2) Sina+(1/2) COSA = (√ 6+√ 2)/4, that is, sin (a+30) = (√ 6+√ 2)/4 = sin75 = sin105.