Calculating bias

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Hi, I have a normally distributed random variable X ∼ N(μ,σ2) with an iid random sample size of n = 3 (X1, X2, X3)
I'm trying to calculate the bias of my estimators for u
ûa : (X1 + X2 + X3)/3 and ûb: (X1 + 4X2 + X3)/6
I know that if u = û then it is unbiased but I'm not sure how to go about doing this.
Any help would be appreciated!