Help with homework

On a homework assignment, I have a data set with the variables (in SPSS)
1) Age
2) Reactiontime (continuous)
3) drug (Placebo, or drug condition)
4) Amount of drug metabolites in their blood (continuous)
5) Subject number (1-20)
6) A median split dichotomous variable on drug levels (0 below median, 1 above median)

I am to "Move the data set around so I can do a dependent samples t-test using reaction time as the test variable and drug as repeated measures variable and send my teacher the data set" I am then to compare it to the independent samples t test.

Firstly, what does he mean by move the data set around, and how would I expect this to compare to my independent samples t test I ran in the previous problem?