Which of the following sets is closed under subtraction?

rational numbers
positive odd numbers
prime numbers
none of the above

Ill mark the brainliest if you me with the these three questions 7,8,9

Solve each quadratic equation by factoring and using the zero product property. x^2 - 8x + 30 = 3x

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!