You must first normalize this in order to use a Z-score table. To convert what you have into a Z score you must use this formula: (x- mean) /standard deviation. In your case (334-310)/12=2. So now you want the probability that a score is greater than 334, which in turn means you want P(Z>2)=1-P(Z<2)=1-.9772=0.0228=2.28%.
