|t + 4| = 12  Therefore t + 4 = +12 or t + 4 = -12  Therefore t = 8 or t = -16
If you place those values back into the equation you find that you will get the correct results.
|t + 4| = 12 →|8 + 4| = 12 or |-16 + 4| = |-12| = 12 return