What is the answer?i don’t understand

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.