I think the answer is "the denominator"
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%.
D^2 - 4d = 3d
d^2 - 7d = 0
d(d - 7) = 0
d = 0 or d - 7 = 0
d = 0 or d = 7
Apologies for the bad handwriting.
