Teresa estimates that the height of a giraffe in a zoo is 18 feet. In fact, it is 16 feet tall. What is Teresa's percent error? Use proportional relationships to solve the problem. Show all your work and round your answer to the nearest tenth.
To find Teresa's percent error, we need to find the difference between her estimate and the actual value, and then divide that difference by the actual value.
The difference between Teresa's estimate and the actual value is $18-16=2$.
To find the percent error, we divide the difference by the actual value: $\frac{2}{16}=0.125$.
Since we want the answer rounded to the nearest tenth, the percent error is approximately $\boxed{12.5\%}$.