Can someone tell me how to do this? i'm doing test corrections. so can someone tell me what the right answer and why it's right because i dont understand it.

8) The graph shows all x values between 2 and 6, including 2 and 6 as well.  We note this in mathematics as: [2,6]

So the answer is C.

9) I can't really read the problem too well because the text is too small.

But anyway, in total he has 399 points so far.  He will take another quiz, let's call that "x".  His average will then be (399+x)/6 (because there are 6 quizzes).

This average needs to be between 80 and 83.  So we need to solve:

80 < (399+x)/6 < 83

Solve:

480 < 399 + x < 498

81 < x < 99

So he needs to get a score of higher than 81 but less than 99.  The only possibility looks like whatever number you circled.

the answer is d. 75%