To calculate Teresa's percent error, we can use the following formula for percent error:
\[ \text{Percent Error} = \left( \frac{|\text{Estimated Value} - \text{Actual Value}|}{\text{Actual Value}} \right) \times 100 \]
Given:
- Estimated Value = 18 feet
- Actual Value = 16 feet
First, we find the absolute difference between the estimated value and the actual value:
\[ |\text{Estimated Value} - \text{Actual Value}| = |18 - 16| = 2 \text{ feet} \]
Next, we substitute the values into the percent error formula:
\[ \text{Percent Error} = \left( \frac{2}{16} \right) \times 100 \]
Now, we calculate the fraction:
\[ \frac{2}{16} = 0.125 \]
Next, we multiply by 100 to convert this to a percentage:
\[ 0.125 \times 100 = 12.5 \]
Thus, Teresa’s percent error is approximately:
\[ \boxed{12.5%} \]