Parallelogram abcd has vertices at a(0,0), b(4,5), c(8,0), d(-4,-5) which conclusion can be made?

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”?