To find the percentage of the seats filled by the 6th graders, we can use the formula for percentage:
\[ \text{Percentage} = \left( \frac{\text{Part}}{\text{Whole}} \right) \times 100 \]
In this case, the "Part" is the number of seats filled by the 6th graders (1078 seats) and the "Whole" is the total number of seats in the theater (3080 seats).
Now, substituting the values into the formula:
\[ \text{Percentage} = \left( \frac{1078}{3080} \right) \times 100 \]
First, calculate the division:
\[ \frac{1078}{3080} \approx 0.350649 \]
Next, multiply by 100 to convert to a percentage:
\[ 0.350649 \times 100 \approx 35.0649 \]
Rounding to the nearest hundredth, we get:
\[ 35.06 \]
Thus, the percentage of the seats in the theater filled by the 6th graders is approximately
\[ \boxed{35.06%} \]