The answer is 97. The first expression is 1+4=5. In the next expression, both numbers are increased by 1 while their sum is increased by 7: (1+1)+(4+1) = (5+7). 2+5=12. In the next expression, both numbers are increased by 1 again, but the sum is increased by the next odd number (which is 9): (2+1)+(5+1)=(12+9). 3+6=21. So, the series will look like this: 1+4=5. 2+5=12. 3+6=21.4+7=33. 5+8=46. 6+9=61. 7+10=78- 8+11=97.
