There are two answers: by added by or subtract I assume you mean plus or minus sign, This is shown by a plus sign with a single line under it (+) ? if so then there are two answers.
9 1/6 - 3 1/2= 55/6 - 7/2= 17/3 or 5 2/3
9 1/6 + 3 1/2 = 55/6 + 7/2 = 38/3 or 12 2/3
Im assuming the sign your talking about is plus or minus + you use this alot in higher math.