Cramer's Rule uses determinants to solve systems and was named after the wacky guy on Seinfeld.  (OK, I made that last part up.)

Let's just do one and I'll show you how it works:

First, we'll get the determinant of the coefficient matrix -- we'll call it D:

Now, we're going to find two more determinants.

The first one we'll call

-- here's how it goes:

Take D...

and delete the column for the x guys...

Replace that column with the " = guys " (the 7 and the -2) and you get

To get the x part of our (x, y) solution, we take