A company sends its employees to a psychologist to try to improve their sales productivity. The following table shows the sales figures, in thousands of dollars, of six employees before and after seeing the psychologist.

Test, at the 5% significance level, whether the visits to the psychologist have improved sales productivity, assuming the increases in sales are normally distributed.

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R D E F Before 10 8. 15 38 60 90 After 14 16 42 80 83