20. brand were Suppose that two brands of gasoline were being compared for mileage. Samples of each were taken and used in identical cars under identical conditions. Nine tests were made of Brand I...

Hi, please see attached. Having trouble with the calculation of the significance test of this problem. Thanks.

Extracted text: 20. brand were Suppose that two brands of gasoline were being compared for mileage. Samples of each were taken and used in identical cars under identical conditions. Nine tests were made of Brand I and six tests of Brand II. The following miles per gallon were found. Brand Brand II 13 15 16 18 15 23 17 14 19 21 16 17 12 13 Are the two brands significantly different? What must be assumed here in order to carry out h test?