Do the Math: Secrets, Lies, and Algebra

In the eighth grade, 1 math whiz < 1 popular boy, according to Tess's calculations. That is, until she has to factor in a few more variables, like:
1 stolen test (x),
3 cheaters (y),
and 2 best friends (z) who can't keep a secret.
Oh, and she can't forget the winter dance (d)!

Then there's the suspicious guy Tess's parents know, but that's a whole different problem.

Can Tess find the solutions?