Solution:

The point C is CD⊥AB, and the vertical foot is D.

Let AD = X, then BD = 20× 50-x =1000-x.

∠∠EAC = 60

∴∠CAB=90 -∠EAC=30

In Rt△BCD,

∠∠FBC = 45

∴∠CBD=∠BCD=45

∴CD=BD= 1000-x

In Rt△ACD,

∫∠CAB = 30

∴cd=tan30× A.D.

That is 1000-x = (√ 3/? 3)x

Solution: x = 1500-500 √ 3.

∴cd=bd=ab-ad= 1000-( 1500-500√3)=500√3-500=500(√3- 1)≈366m

A: The distance from Building C to AB Expressway is about 366 meters. ..