Quote from november551
If both tests are evenly weighted, you're up to an 80%
I think she just added to her average, so depending on how many different items comprise her average (how many test, ect..) will determine how much that 89 will bring her average up.
Just add up all of your test and divide by the number of test and that will give you your average. If there's more to your grade then you'd have to figure how much each item is weighted towards your average.
So if your average consisted of a couple test, then the 89 will probably bring it up a decent amount, nothing huge, but probably enough to bump you past passing. On the other hand, if this is like your fifth test among a bunch of quizzes, or something like that, then it won't affect your grade as much.
So with the given advice among these past few post you should be able to at least guesstimate your average.
Oh, and if there are test ahead of you, don't worry about it as much, just make sure to do good on them and your sure to pass the passing point.