∴AD=CDcot∠CAD=423 meters,

In Rt△BCD, CD = 42m, ∠ CBD = 45,

∴AD=CDcot∠CBD=42 meters,

∴AB=AD-BD=42(3- 1) meters;

(2) Speed =42(3? 1) 2 = 21(3-1) m/s ≈55. 19 km/h,

∵55. 19