The graph of the function f is shown below. How many solutions does the equation f(f(x)) \equal{} 6 have?
[asy]size(220);
defaultpen(fontsize(10pt)+linewidth(.8pt));
dotfactor=4;pair P1=(-7,-4), P2=(-2,6), P3=(0,0), P4=(1,6), P5=(5,-6);
real[] xticks={-7,-6,-5,-4,-3,-2,-1,1,2,3,4,5,6};
real[] yticks={-6,-5,-4,-3,-2,-1,1,2,3,4,5,6};draw(P1--P2--P3--P4--P5);dot("(-7, -4)",P1);
dot("(-2, 6)",P2,LeftSide);
dot("(1, 6)",P4);
dot("(5, -6)",P5);xaxis("x",-7.5,7,Ticks(xticks),EndArrow(6));
yaxis("y",-6.5,7,Ticks(yticks),EndArrow(6));[/asy]<spanclass=′latex−bold′>(A)</span>2<spanclass=′latex−bold′>(B)</span>4<spanclass=′latex−bold′>(C)</span>5<spanclass=′latex−bold′>(D)</span>6<spanclass=′latex−bold′>(E)</span>7