It says what is the probability student doesn't have lice GIVEN THAT student tested negative.
<em>We need to look at the tree branch that has "student has no lice" and "test shows negative".</em>
<em><u>Looking at the bottom-most branch, we see this one shows that "test is negative and student has no lice". This has a value of 0.6768. This is the correct answer.</u></em>
