Is this subtracting or adding? all i know its a 180 degree angle i think

So if you're trying to find the other section of the 128 degree angle that isn't taken up by the 33 degree angle, or LHI, you just subtract 33 from 128. This is because you need to find the angle GHI without the part GHL, so just subtract that part away.

128 - 33 = 95

So therefore angle LHI is equal to 95.