Is it possible to solve this?

Hm.

Wouldn't it be..

Code:

(7x-3y)^2-6 = 7
7x-3y = sqrt(13)
-3y = sqrt(13)-7x
y = -((sqrt(13)-7x)/3)

Or am I doing something wrong?

Yeah. I just distributed the -3.

(I didn't say that 7 divided by 3 was 21....YOU DIDN'T SEE ANYTHING! -Fixes it-)