The given sum is
[tex]11+17+23+29+35+41[/tex]
The common difference is 17-11=6.
The given sum can be written as follows.
[tex]11+17+23+29+35+41=(5+6)+(5+2\times6)+(5+3\times6)+(5+4\times6)+(5+5\times6)+(5+6\times6)[/tex]
Consider the last term
[tex]5+6\times6[/tex]
Here multiple of 6 is 6
So, the maximum value of i is 6.
The answer is
[tex]\sum ^6_{i\mathop=1}(5+i\times6)[/tex]
