What is 50xx?
To graph the two equations, first solve both for y. Then you go to the "y = " screen and put them into y1 and y2. Then go to your "graph" screen.
To solve your linear equation, type in
simultd([2,3;-8,-12],[6;-24]) then ENTER.
You should get Error:Singular Matrix.
That's because one is a multiple of the other. There both essentially the same.
Another way is to use RREF([2,3,6;-8,-12,-24]).
You should get a row of 0's at the bottom. That' no good.