This is my code.
\documentclass[13pt,a4paper]{scrartcl}
\usepackage[x11names]{xcolor}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.12}
\usetikzlibrary{intersections}
\begin{document}
\begin{center}
\begin{tikzpicture}[scale=1.2]
\begin{axis}[axis lines=middle,xmin=-0.5,xmax=180,ymin=-0.5,ymax=150,
x post scale=1.5,
y post scale=2]
\addplot+[no marks,domain=0:120,samples=200, ultra thick, color=DarkOliveGreen4] {x} node[right,pos=1] {45};
\addplot+[no marks,domain=50:150,samples=200, ultra thick, color=Gold3] {-0.25x+112.5} node[below] {$\pi = 20%$};
\addplot+[no marks,domain=50:150,samples=200, ultra thick, color=gray] {-0.66667x+133.333} node[below] {$\pi = 40%$};
\addplot+[no marks,domain=50:100,samples=200, ultra thick, color=Gold3] {-1.5x+175} node[below] { $\pi = 60%$};
\addplot+[domain=70:120,samples=200, color=DodgerBlue2, mark=none, ultra thick] {((9.4868-0.2sqrt(x))/0.8)^2};
\addplot+[domain=55:120,samples=200, color=DodgerBlue2, mark=none, ultra thick] {((8.3666-0.6sqrt(x))/0.4)^2};
\addplot+[domain=55:120,samples=200, color=DodgerBlue2, mark=none, ultra thick] {((8.944271-0.4sqrt(x))/0.6)^2};
\filldraw (50,100) circle (2.5pt)node[right,font=\tiny] {};
\filldraw (90,90) circle (1.5pt)node[right,font=\tiny] {};
\filldraw (80,80) circle (1.5pt)node[right,font=\tiny] {};
\filldraw (70,70) circle (1.5pt)node[right,font=\tiny] {};
\end{axis}
\end{tikzpicture}
\end{center}
\end{document}
This is the image. I like to have all lines solid always, as long as I don't ask for another style. There are some similar questions. None did solve my problem.

