first of all , the reference angle is 30 degrees . But sin is negative so it would be in the 3rd and 4th quadrant ie

x=210 , 330

for

reference angle = 30 degrees and since cos is negative , it will be in the 2nd and 3rd quadrant .

ie 3x=150 , 210 , 510 , 570 , 870 , 930

x=50 , 70 , 170 , 190 , 290 , 310

Assuming that 0<x<360 , then 0<3x<1080