ClearAll;
$DefaultFont = {"Times-Roman",10};
Needs["Graphics`Graphics`"];
P[x_,y_]:= 9 (x^(5/3) y^(-3/2))/250;
f[x_]:= P[x,0.3];
g[y_]:= P[0.8,y];
fp[x_]:= Evaluate[D[f[x],x]];
gp[y_]:= Evaluate[D[g[y],y]];

plottl = Plot[f[x],{x,0.1,1},
			  PlotRange -> {{0,1.01},{0,f[1]}},
			  AxesLabel -> {"x","z"},
			  PlotLabel -> "(a)    z  =  f(x)  =  P(x,0.3)"];
plottr = Plot[g[y],{y,0.1,1},
			  PlotRange -> {{0,1.01},{0,g[0.1]}},
			  AxesLabel -> {"y","z"},
			  PlotLabel -> "(b)    z  =  g(y)  =  P(0.8,y)"];
plotbl = Plot[fp[x],{x,0.1,1},
			  PlotRange -> {{0,1.01},{0,fp[1]}},
			  AxesOrigin->{0,-0.02},
			  AxesLabel -> {"x","z"},
			  PlotLabel -> FontForm["z = f'(x)",{"Courier",10}]];
plotbr = Plot[gp[y],{y,0.1,1},
			  PlotRange -> {{0,1.01},{gp[0.1],0}},
			  AxesOrigin->{0,-12.25},
			  AxesLabel -> {"y","z"},
			  PlotLabel -> FontForm["z = g'(y)",{"Courier",10}]];			  
Show[GraphicsArray[{{plottl,plottr},{plotbl,plotbr}}],
				PlotLabel -> "Figure 25.2"]