ANSWER :
The sum of 12th terms is 78.
STEP BY STEP EXPLANATION :
Sn = [(A1 + An) × n]/2
S12 = [(1 + 12) × 12]/2
S12 = [13 × 12]/2
S12 = 156/2
S12 = 78
Therefore , the sum of 12th terms is 78.
