"The final prices from an online auction for 2 sales methods are shown below. Construct a 95% confidence interval for comparing the 2 pop means.

1.buy it now option- 220, 200, 225, 240, 225, 210, 225

2.bidding option- 255, 262, 225, 248, 265, 231, 228, 258, 248, 263, 204, 211, 226, 220, 225, 230, 214, 229

We are supposed to use our calculators to do the problem and I must be doing something wrong. I am using 2 sample t interval and keep getting (-28.91, -.99) when the answer is ( -31.13, 1.21)

What am I entering wrong? thank you