In the summation, we have n equals 3 and upto 7.
To expand the summation, substitute the value of n in the function from 3 to 7,
[tex](3+4)=7[/tex][tex](4+4)=8[/tex][tex](5+4)=9[/tex][tex](6+4)=10[/tex][tex](7+4)=11[/tex]
Thus the expansion is
[tex]7+8+9+10+11[/tex]
The correct option is a.
