Whats x-y=-3 and whats 2x+y =12

Landon wrote that 3−2.6=4. which statement about his answer is true?

Scores on a university exam are normally distributed with a mean of 78 and a standard deviation of 8. the professor teaching the class declares that a score of 70 or higher is required for a grade of at least “c.” using the 68-95-99.7 rule, what percentage of students failed to earn a grade of at least “c”?

Factor the following expression completely 6x^11-24x^7