The fallen tree and the ground make a right-angled triangle with the side opposite the 40 degree angle = 10 ft and the hypotenuse is the length of the tree above 10 ft.
So sin 40° = 10 / x where x is the hypotenuse.
x = 10 / sin 40°
x = 15.56 ft
So the height of the tree was 10 + 15.56 = 25.56 feet (answer).
