Help me please i dont understand this n im in a quizz

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”?

What is the approximate value of  x  in the equation below.–3.396–0.7080.3040.955

Hundred and tens tables to make 430 in five different ways