Researchers wished to know if they could conclude that two populations of infants differ with respect to the average ages at which they walked alone. Assuming that the age at which the infant walked alone is normally distributed for two populations. The following data (ages in months) were collected:

Population A

sample size A: 16

sample mean A: 12

sample variance A: 4.00

Population B

sample size B: 9

sample mean B: 14

sample variance B: 12.00

Assuming that the variances of age at which the infant walked alone for two populations are different, for testing hypotheses H₀: _A- _B 0 vs. H₁: _A- _B< 0 at 0.05 level of significance, what is the upper bound of the critical region for the test?