Since you are to find the angle wherein sine is negative and that it is equal to -√3/2
remember that sine can only be negative if it is at the 3rd and 4th quadrant. and the angle based on the unit circle with sine being -√3/2 is 60degrees.. finding the two angles you'll have:
at the 3rd quadrant
180 + 60 = 240degrees
at the 4th quadrant
360 - 60 = 300degrees