Answer:

"Gov" refers to "Student Government".
==================================================
Step-by-step explanation:
The rows are labeled "7th grade", "8th grade" and "Total".
The columns are labeled "Music", "Student Government", "Theater", "Sports", and "Total".
I'll abbreviate "Student Government" to "Gov" so that the table doesn't get too wide.
There are 254 students total. This value goes in the bottom right corner of the table. This is the grand total.
----------
We have 80 students in music. This value goes at the bottom of the "music" column since we're in a "total" row. Basically it's the total of all the music students regardless of grade.
Of those 80 students in music, 42 are in seventh grade. Write 42 in the first row of this column and 38 just underneath it (because 80-42 = 38). The two values 42 and 38 should add to the 80 mentioned.
----------
There are 21 students in student government. This value goes at the bottom of the "student government" column.
9 of these students are in eighth grade, so the remaining 21-9 = 12 must be in seventh grade.
----------
There are 65 students in theater. This value goes at the bottom of the "theater" column.
There are 20 such students in 7th grade and 45 in 8th grade (because 65-20 = 45).
----------
There are 88 students in sports.
30 are in 8th grade, so 88-30 = 58 must be in 7th.
----------
At this point, you should have these values along the bottom row:
80, 21, 65, 88, 254
The first four values (80, 21, 65, 88) should add to the grand total 254.
Along each row, add up the values to get the row total.
7th grade: 42 + 12 + 20 + 58 = 132
8th grade: 38 + 9 + 45 + 30 = 122
There are 132 seventh graders and 122 eighth graders.
Those subtotals add to 132+122 = 254 total students, which helps confirm we did things correctly.