How to find out my exam mark from my average?

So, my exam mark has not been released but my average has. From looking at the syllabus and the assignment I already have done, I know I should be looking at something like this:

90 = 0.2(93) + 0.15(80+) + 0.1(exam)

...where all the 0.somethings are what that mark is worth, or weighted as. (The 80+ is a guess. It's a participation mark. I have no idea what I got, but probably high.)

Here's where I get stuck. It's only midyear, so all the 'weights' only add to 45% of my final mark. So... I can't just plug in the numbers and get my exam, because of that other 55%. Do I represent by a .55(1)? Do something else entirely?

Help?
 
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