16 out of 24 would equal around 67%, and that as a grade would be a D.
However, grades MAY vary from school to school.
But on average:
A= 100 through 90, B= 89 through 80, C= 79 through 70, D= 69 through 60, and an F= 59 and below that.
Keep in my mind that if your grade has digits after the decimal, it will be rounded (in your case) and that may also change your grade, for example if your grade is 79.7%, then it will be rounded to 80%, and your grade will be a B.
C because it has the x variables in the numerator. This is wrong because the x axis represents horizontal movement and slope is rise over run, not run over rise