Question 618529
It's 2 straight lines.
x+y=4
Find 2 points.  Pick values for x or y and find the other variable.  Zero usually works well.
Plot the 2 points.
Draw a line thru them.
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Do the same for the other equation.
Where they intersect is at the values of x & y that fit both equations.
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dl the FREE graph software at
http://www.padowan.dk
Use F6 to enter them as they are.