50, 看这儿

since we know AE and ED, so we easily know the length of AD=BC= sqrt(21^2+72^2)= 75and CF=sqrt(75^2-45^2)=60,

let's draw a line parallel to AD pass point F, it interacts with AD at point G, and interacts with BC at point H,

then found length of FH=36 and BH=AG=27, then we found GH= 14 in triangle of GFD,

AB=FH+GF=36+14=50.