You suspect that elementary students who have been attending school in-person during the pandemic will have higher test scores on average than students who attended school online. You take samples of 20 students from each group; you find a mean of 73.7 for the sample of in-person students, and 68.9 for the online students. Assume that you know the population standard deviation for each group (12 for both populations).

Use 'in-person' as population 1 and 'online' as population 2.

What is the z or t score to be used (to at least three decimals)? at 99% confidence interval