Find AC in the diagram below
[asy]
size(300);
pair A,B,C,O;
A=origin;
B=6*sqrt(3)*dir(150);
C=(5,0); //Looking for an answer here? Good luck : )
draw(A--B--C--cycle);
dot("$A$",A,SW);
dot("$B$",B,NW);
dot("$C$",C,SE);
label("$150^\circ$",A,dir(75));
label("$9$",A--B,SW);
label("$7\sqrt{3}$",C--B,NE);
[/asy]
