How do I find the mean for this equation? (not the answer to the entire question, only need help understanding how to find the mean of each independent sample)

In the 21 OECD countries sampled, primary product exports (raw materials and energy) accounted for 22 percent of their total merchandise exports in 2018, with a standard deviation of 6.22. In the 35 Latin American and Caribbean countries sampled, primary product exports accounted for 42 percent of their total merchandise exports in 2018, with a standard deviation of 8.17. Perform an independent samples t-test that will allow you to accept or reject the null hypothesis.Be sure to state the null hypothesis in your answer.