Given, →F=→i+→j+→k.
Let, the position vector of A is (3,3,3) with respect to the origin O and that of B is (4,4,4).
Then, →OA=3→i+3→j+3→k and →OB=4→i+4→j+4→k .
Now, →AB= →OB - →OA=→i+→j+→k.
→F is in the direction of displacement →AB.
So, work done =→F.→AB
=(→i+→j+→k).(→i+→j+→k)=3 unit.