To calculate the percentage of students in Mrs. Guajardo's first-period class who reported math as their favorite subject, we first need to identify how many students from the 21 surveyed chose math as their favorite.
From the table:
- English: 6
- Math: 4
- History: 3
- Science: 5
- Other: 3
The number of students who reported math as their favorite subject is 4.
Next, we calculate the percentage of students who chose math:
\[ \text{Percentage} = \left( \frac{\text{Number of students who like math}}{\text{Total number of students surveyed}} \right) \times 100 \]
Substituting in the numbers:
\[ \text{Percentage} = \left( \frac{4}{21} \right) \times 100 \approx 19.05 \]
Rounding this to the nearest whole number, we have:
\[ \text{Percentage} \approx 19% \]
Thus, the percentage of students in the sample who reported math as their favorite subject is 19%.