Here's a plot for Mathematica that you can use as a template to plot ListLinePlot and Plot in the same figure. Font sizes are increased to be well visible in a research article.
xmax = 150; ymax = 0.025; Show[ ListLinePlot[{Table[{t, PDF[GammaDistribution[3.715287738432738`, 16.575007504627795`]][ t]}, {t, 0, xmax, xmax/10}], Table[{t, PDF[GammaDistribution[6.502676225156808`, 8.60919186301341`]][ t]}, {t, 0, xmax, xmax/10}], Table[{t, PDF[GammaDistribution[3.3444580518527207`, 16.73897127052263`]][ t]}, {t, 0, xmax, xmax/10}]}, PlotRange -> {{0, xmax}, {0, ymax}}, PlotLabel -> PDF, AxesLabel -> {Style["SIR", 16, Bold], Style["", 16, Bold]}, PlotLegends -> Placed[{"Sim 1", "Sim 2", "Sim 3"}, Right], PlotMarkers -> {Automatic, 10}, BaseStyle -> {FontSize -> 15}], Plot[ { PDF[GammaDistribution[3.715287738432738`, 16.575007504627795`]][ t], PDF[GammaDistribution[6.502676225156808`, 8.60919186301341`]][t], PDF[GammaDistribution[3.3444580518527207`, 16.73897127052263`]][t] }, {t, 0.01, xmax}, PlotStyle -> Thick, PlotLegends -> Placed[{"\[CapitalGamma](3.7, 16.6)", "\[CapitalGamma](6.5, 8.6)", "\[CapitalGamma](3.3, 16.7)"}, Right]] ]
Output:
References: