You have the next situation:
As the building and its shadow form a angle of 90º (right angle), you use the Pythagoras theorem:
[tex]x=\sqrt[]{h^2-s^2}[/tex]
The measure of x is equal to the square root of hypothenusa squared less the shadow measure squared:
[tex]\begin{gathered} x=\sqrt[]{(250ft)^2-(245ft)^2} \\ x=\sqrt[]{62500ft^2-60025ft^2} \\ x=\sqrt[]{2475ft^2} \\ x=49.749ft\approx49.7ft \end{gathered}[/tex]Then, the building is 49.7 feet tall
