What is the first step to solve the following system of equations using substitution? x - y = 12
2x - y = 12
A.) Add the two equations together.
B.) Solve the first equation for x.
C.) Multiply the first equation by 2.
D.) Divide the second equation by 2.

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”?