The number of lines that can be formed for the next concert is 78.
Using the parameters given for our Calculation; 
- Number of students = 156 
 - Numbers of students per line = 2 
 
To obtain the number of lines that can be formed; 
- Number of students / Number of students per line 
 
Now we have; 
Number of lines = 156 / 2 = 78
Therefore, the number of lines that can be formed is 78