data = {{2200, 5}, {1700, 10}, {1050, 20}, {640, 50}, {420, 100}};
lm = LinearModelFit[data, {rpm^3, rpm^2, rpm}, rpm];

data1 = {{600, 5}, {800, 10}, {400, 20}, {640, 50}, {440, 100}};
  lm1 = LinearModelFit[data1, {rpm^3, rpm^2, rpm}, rpm];

Show[ListPlot[{data, data1}, Filling -> Bottom],
 ListLinePlot[{data, data1}],
 Plot[lm[rpm], {rpm, 0, 125}, PlotLabel -> {"Natural"},
  AxesLabel -> {rpm, [Mu]}, PlotLabels -> {"A6", "A7"}]]