9514 1404 393
Answer:
678
Step-by-step explanation:
The sequence has a first term of 12 and a common difference of 21-12 = 9. The explicit formula for the n-th term is ...
an = a1 +d(n -1)
For a1 = 12 and d = 9, this is ...
an = 12 + 9(n -1)
Using 75 for the value of n, we have ...
a75 = 12 + 9(75 -1) = 12 + 666 = 678
The 75th term is 678.
