Given following Series objects: (a) What will be the result of S1 + S2 ?

 S1                      S2                
0      3                 0     12                
1      5                 2     10               
2      6                 3     15                
4      10                4     20               
5      12                6     27

Ans:

0     15
1     NaN
2     16
3     NaN
4     30
5     NaN
6     NaN