Question 639953
Hint: Since y = 2x-4, you can replace the <font color="green">y</font> in the first equation with <font color="red">2x-4</font>


3x-y =7


3x-(y) =7


3x-(<font color="green">y</font>) =7


3x-(<font color="red">2x-4</font>) =7


3x-(2x-4) = 7


I'll let you take it from here.