Question 888363
The building is 40 feet tall.  That's one side of your right triangle.  The post is 30' from the building.  That's your second side.  You're asked to find the hypotenuse in this triangle.
{{{a^2}}}+{{{b^2}}}={{{c^2}}}
40^2 + 30^2 = {{{c^2}}}
1600 + 900 = {{{c^2}}}
2500 = {{{c^2}}}
Take the square root of each side to get
50 = c
The pole is 50 feet long.