The first equation tells you that writing "y" is the same as writing "4x-1".
So, in the second equation, you can substitute "y" with "4x-1":
[tex]y=2x-5\mapsto 4x-1=2x-5 \iff 2x=-4 \iff x=-2[/tex]
Now that we have the value for x, we can deduce the value of y:
[tex]y=2x-5 = 2(-2)-5 = -4-5 = -9[/tex]
