#### Answer

The distance of the ladder from the building is \[15\text{ft}\].

#### Work Step by Step

The height of the building against which ladder is placed is 20ft and the length of the hypotenuse is 25ft. The length of ladder from the building can be calculated by using the Pythagorean Theorem
Compute the distance of the ladder from the building using the equation as shown below:
\[\begin{align}
& {{a}^{2}}+{{b}^{2}}={{c}^{2}} \\
& {{20}^{2}}+{{b}^{2}}={{25}^{2}} \\
& 400+{{b}^{2}}=625 \\
& {{b}^{2}}=625-400
\end{align}\]
\[\begin{align}
& {{b}^{2}}=225 \\
& b=\sqrt{225} \\
& b=15\text{ft}
\end{align}\]
Hence, the distance of the ladder from the building is \[15\text{ft}\].