Independent random samples from two regions in the same area gave the following chemical measurements (ppm). Assume the population distributions of the chemical are mound-shaped and symmetric for these two regions.

Region I:x1;n1=12

438 1013 1127 737 491 840 306 402 1155 1075 500 340

Region II:x2;n2=16

778 464 563 610 827 894 476 394 824 387 816 767 479 710 389 826

Letmean 1 be the population mean forx1 andmean 2 be the population mean forx2. Find a 90% confidence interval formean 1 - mean 2