Picture a right triangle.  Moon's distance is the base, moon's diameter is the height.  Long base, small height.  Angle between base and hypotenuse is 00087 radians.  Height / base is tangent of that angle.  so tan(0.0087) = 3500 / distance.  rewrite as distance = 3500 / tan(0.0087) and solve with calculator.  answer should be in ballpark of 240,000 miles which is 384,000 km.