Can someone show me how to answer this type of question? (100 points)

Simplify 24÷(-2)(3)+7 a. -29 b. 3 c. 11

Extra points! find the missing dimension! need asap

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”?