The work done by the force $\overrightarrow {f}=\overrightarrow{i}+\overrightarrow{j}+\overrightarrow{k}$ acting on a particle, if the particle is displaced from $A(3 , 3 , 3 )$ to the point $B(4 , 4 , 4 )$ is

Question

$$\begin{array}{1 1}(1) 2 units &(2)3 units\\(3) 4 units &(4) 7 units\end {array}$$