Answer:
276 seats
Step-by-step explanation:
If a concert hall has 12 seats in the first row, 14 seats in the second row, 16 seats in the third row and the pattern continues, each row will have 2 more seats than the previous row. So, the number of seats in each row from the first to the 12th row are:
12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, and 34
Then, the number of seats un the first 12 rows are:
12 + 14 + 16 + 18 + 20 + 22 + 24 + 26 + 28 + 30 + 32 + 34 = 276
Therefore, the answer is 276 seats.