M-x package-install RET gnuplot RET
# Set the title for the graph
set title "Plot of functions"
# Label the axes
set xlabel "x"
set ylabel "f(x)"
# Set the range for x (you can adjust the range as needed)
set xrange [0:5000]
set yrange [0:5000]
# Plot the functions
plot x title "x", \
15 + 0.8*x title "15 + 0.8 * x", \
240 + 0.6*x title "240 + 0.6 * x"