Assume a researcher designs an experiment about the IAS and the RDY (intermediate Algebra Skills (IAS) test and Calculus

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Assume a researcher designs an experiment about the IAS and the RDY (intermediate Algebra Skills (IAS) test and Calculus Readiness (RDY) of the Descriptive Tests of Mathematical Skills (DTMS)) scores. A group of people randomly chosen from the USA and took both tests; first the IAS and then the RDY test. The researcher is interested in whether or not the group did significantly worse on the RDY after taking the IAS. H0: uIAS ≤ uRDY vs. HA: uIAS > uRDY (a= 0.05). Assume the population she sampled from was normally distributed (based on ETS reports) with means (uIAS and uRDY) that are equal and non zero standard deviations (oIAS and oRDY) that are also equal, it is a "random" sample, the observations were independent, the sample is large, and there was no measurement error. What is the correct distribution test used?