import graph; 
 
size (7cm,0); 

real a=-1, b=-.1, c=1.5;
real f(real x) {return (x-a)*(x-b)*(x-c);}
draw(graph(f,b-.5,c+.3)); 

xaxis (Ticks("%", new real[]{a,b,0,1,c},Size=1mm,1bp+red)); 
labelx("$b$",b,SW);
labelx(0,1.5N);
labelx(1,1.5N);
labelx("$c$",c,SE);