A burger at Ricky C's weighs 120 grams, of which 30 grams are filler. What percent of the burger is not filler?

$\textbf{(A)}\ 60\%\qquad
\textbf{(B)}\ 65\% \qquad
\textbf{(C)}\ 70\%\qquad
\textbf{(D)}\ 75\% \qquad
\textbf{(E)}\ 90\%$
1. First, we need to determine the weight of the burger that is not filler. Given that the total weight of the burger is 120 grams and 30 grams are filler, we can calculate the weight of the non-filler portion as follows:
   \[
   120 \text{ grams} - 30 \text{ grams} = 90 \text{ grams}
   \]

2. Next, we need to find the percentage of the burger that is not filler. We do this by dividing the weight of the non-filler portion by the total weight of the burger and then multiplying by 100 to convert it to a percentage:
   \[
   \frac{90 \text{ grams}}{120 \text{ grams}} \times 100\% = 0.75 \times 100\% = 75\%
   \]

3. Alternatively, we can calculate the percentage of the burger that is filler and then subtract that from 100% to find the percentage that is not filler. The percentage of the burger that is filler is:
   \[
   \frac{30 \text{ grams}}{120 \text{ grams}} \times 100\% = 0.25 \times 100\% = 25\%
   \]
   Therefore, the percentage of the burger that is not filler is:
   \[
   100\% - 25\% = 75\%
   \]

\(\blacksquare\)

The final answer is \( \boxed{ 75\% } \)