I assume you mean...,
12X - 5Y = 30
Y = 2X - 6
You are given Y, so insert it into the top equation above.
12X - 5(2X - 6) = 30
12X - 10X + 30 = 30
2X = 0
X = 0
=====so, obviously,
Y = - 6
======Check.
12(0) - 5(- 6) = 30
30 = 30
========checks
(0, - 6)
=======Ordered pair.