The first thing you want to do is find out what the sqrt(7) is. Use your calculator to do this. Most calculators do it this way
7
^ or y^x or x^y or some calculators do it with a √ key see below.
0.5
=
You should get 2.64 something. If your calculator has a √ key you do it as
√
=
Regardless of that, the answer you should get is 2.64. The friend certainly did not do that. A and C are both wrong for the same reason.
What the friend did was divide by 2. So the right answer is B.