We need the Z-scores for the two limits:
Z1=(9.08-9.12)/0.15=-0.2667; Z2=(9.16-9.12)/0.15=0.2667.
Z1=0.3949, Z2=0.6051. So the difference is 0.2102 or 21.02%.
There's about a 21.02% probability that the average weight of 3 9oz bags of chips will lie between 9.08 and 9.16 ounces (within 0.04oz of the mean).