Answer: 15.19 feet
Explanation:
Hi, since the situation forms a right triangle (see attachment) we have to apply the Pythagorean Theorem:
c^2 = a^2 + b^2
Where c is the hypotenuse of the triangle (in this case is the length of the plank) and a and b are the other sides.
Replacing with the values given:
16^2 = 5^2 + x^2
256=25 + x^2
256-25 = x^2
231 = x^2
√231 =x
15.19 ft =x
the plank will be 15.19 feet far from the building.
Feel free to ask for more if needed or if you did not understand something.