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Option a

Step-by-step explanation:

Given two normal distribution samples

I group has 106 as mean and 8.5 as std deviation with sample size = 60

II group has 121 as mean and 6.3 as std deviation with sample size =38

We find mean difference =-15

For margin of error finding, we have to find the combined std error for the difference

Variance of difference = Sum of variances

STd error for difference = 1.50

Hence for 99% margin of error =2.58(1.50)

= 3.87