So AD=FE=BC=9 and AB=DC. More info is needed! Let's say AB=a, a known quantity. We also need an angle. Let's pick A=x, another known quantity. The other angles will be: B=180-x=D and C=x. By the cosine rule, in triangle ACD, AC^2=AD^2+DC^2-2AD.DCcosD. So AC^2=81+a^2-18acos(180-x)=81+a^2+18acosx. AC=sqrt(81+a^2+18acosx).
Put x=60° and a=18, then AC=sqrt(81+324+162)=sqrt(567)=9sqrt(7)=23.81.