Let C be the base of the mountain
Consider the Rt triangle ABC in which BC= 3400 Cot74. Hence BD = 930+3400 Cot74
Now consider the Rt triangle ABD in which,
DA2 = (3400)2 + (930 +3400Cot74)2
= (3400)2
+ (930+974.938)2
= (3400)2 + (1904.938)2
= 11560000+ 3628788.7838
=15188788.7838
Hence DA= 3897.2796 ft
****