Answer:
an = 12 + 6(n-1)
Explanation:
The formula for an arithmetic sequence is
an = a1+d(n-1)
where a1 is the first term and d is the common difference
a1 =12
To find d take the second term and subtract the first term
18-12 = 6
Check with the third term and the second term
24 -18 = 6
We add 6 each time
d= 6
an = 12 + 6(n-1)