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To solve this problem, I'll use trigonometric functions,
The trigonometric function that relates the opposite side and the hypotenuse is sine
Formula
sin 48 = Opposite side / hypotenuse
hypotenuse = 105 ft
opposite side = H
Substitution
sin 48 = H/105
Solve for H
H = 105*sin 48
Simplification
H = 105*0.743
Result
H = 78 ft