This format has no function creating function. You can easily graph equations using many browsers. The only reason to "solve" systems of equations graphically is when you can not calculate the solution mathematically. This system is rather simple to solve as it is just two lines...
If a solution exists, y=y, so we can say:
-x+4=-2x+1 add 2x to both sides
x+4=1 subtract 4 from both sides
x=-3, since y=-x+4
y=-(-3)+4
y=3+4
y=7, so the solution to the system of equation, graphically where the two lines intersect, is the point:
(-3, 7)
