task 2

<< graphics`graphics`

S1 = 0.4; S2 = 0.5;

DisplayTogether[Plot[0.3 k - 0.025 k^2, {k, 0, 13}], 
      Plot[S1 (0.3 k - 0.025 k^2), {k, 0, 13}, PlotStyle -> Hue[ .7]], 
      Plot[S2 (0.3 k - 0.025 k^2), {k, 0, 13}, PlotStyle -> Hue[ .1]], 
      Plot[0.1 k, {k, 0, 13}], ImageSize -> 550]