To compare the treatment effect of two medications, two independent samples of patient performance data were collected. The sample sizes are 15 and 18 respectively. Assuming that the two populations shared the same variance, the researchers decided to conduct a two independent samples test for the means. They found that the difference between the two sample means was4.0 and the pooled sample standard deviation of the two samples was 4.2. What would be the obtainedt-value under the null hypothesis that assumes no difference between the two population means?

a) 1.38

b) 2.38

c) 2.72

d) 2.04