Can someone help me?

A triangle has the measurements (x + 4), (x + 8) and (x) degrees. A student wrote this 3 point response.
180 = 180 - x + 180 - (x + 4) + 180 - (x + 8)
180 = 540 - 3x + 12
- 372 = - 3x
x = 124
The ext. angles are 124, 128, and 132 degrees.
The int. angles are 56, 52, and 48 degrees.
The smallest ext. angle is 48 degrees.
What error did the student make?

to find x ur supposed 2 add all the angles nd set it equal to 180: x+4+x+8+x=180. once u know what x is plug it back into the angles nd solve to get the angles. hope I helped