Kite ABCD has right angles at B and D, and AB<BC. Points E∈AB and F∈AD satisfy AE=4, EF=7, and FA=5. If AB=8 and points X lies outside ABCD while satisfying XE−XF=1 and XE+XF+2XA=23, then XA may be written as da−bc for a,b,c,d positive integers with gcd(a2,b2,c,d2)=1 and c squarefree. Find a+b+c+d.