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Which expression can be used to determine the slope of the line that passes through the points -6, three and one, -9

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Plz answer asap! i will reward brainliest and 12 points for these three questions!take notice: these three questions are completely different! 1) what is the percentage of sugar in the syrup made of 10 kg of water and 4 kg of suugar? 2) what was the original price if after 10% discount it became $450? 3) at first a price was decreased by 12%, then it was disounted again by an additional 5%. what is the percent of the total discount? , and remeber i will award brainliest and 12 points!