HI
i will put it in degrees so that its easier for you to see but you will need to change it back to radian s.
tan (3x-30)=-1
3x-30 = 135 , 315 , 495 , 675 , 855 , 1035
x=55 , 115 , 175 , 235 , 295 , 355
the ones in red are the basic angles , the reference angle is 45 , since tan is -ve , it would be in the 2nd and 4th quadrant , then just add 360 for the subsequent angles . Just remember that
0<x<360 , 0<3x<1080