To find out how many eighth graders took the survey, we add the preferences for tacos and pizza among the 8th graders:
- 8th graders who prefer Pizza: 54
- 8th graders who prefer Tacos: 81
Now we can calculate the total number of 8th graders surveyed:
\( 54 + 81 = 135 \)
Therefore, the total number of eighth graders who took the survey is 135.