12.
Given that the length of the ladder is 12 feet and the ladder is placed 4 feet away from the base of the ladder.
We have to find how high the ladder reaches the wall.
From the figure, by Pythagoras theorem, we can say that:
![\begin{gathered} x^2+4^2=12^2^{} \\ x^2+16=144 \\ x^2=144-16 \\ x^2=128 \\ x=\sqrt[]{128} \\ x=11.31 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/k7qohnu2751eoblicovlpg3apiql4jpe9o.png)
Thus, the ladder goes 11.31 feet high on the wall.