Answer: 3657
Explanation:
18-15=3
15-12=3
3 ==> rate of change per term
3*46=138
138-3=135
135+12=147 ==> 46th term
Now find the average of the first and 46th term of the sequence:
(147+12)/2=
159/2=79.5
Now multiply the average by 46 to find the sum of the sequence.
79.5*46=
159*23=3657 ==> sum of 46 terms