Dear,
I would require the plot legend only once.
The program I written is showing it many times, the equation is being solved.
Thank you for help
Plot Legend for ContourPLot.nb (182 KB)
You can do it this way:
PlotLegends -> If[cp == 100, {"Line Equation"}, None]
You may also consider something along this line:
ContourPlot[2 x + 3 y + 50, {x, 10, 20}, {y, 25, 35},
Contours -> Range[100, 250, 5], ContourLabels -> All]
Thanks