What is

2y+6=x

y-3x=-13

If you plug 2y + 6 in x on the second equation, it will be

y-3 (2y+6) = - 13

y-6y-18 = - 13

-5y = 5

y=-1

then you can plug in y in any of the equations to solve for x

(I'll do the first one)

2 (-1) + 6=x

-2+6=x

x=4

x=4 y=-1