The work done by a force $\overrightarrow{\mathrm{F}}=3\hat{\mathrm{i}}-4\hat{\mathrm{j}}+5\hat{\mathrm{k}}$ displaces the body from a point (3,4,6) to a point (7,2,5) is

$\overrightarrow{\mathrm{F}}=3\hat{\mathrm{i}}-4\hat{\mathrm{j}}+5\hat{\mathrm{k}}$

$\overrightarrow{r_2}=7\hat{\mathrm{i}}+2\hat{\mathrm{j}}+5\hat{\mathrm{k}}$

$\overrightarrow{r_1}=3\hat{\mathrm{i}}+4\hat{\mathrm{j}}+6\hat{\mathrm{k}}$

$W=\overrightarrow{F}.\overrightarrow{S}=\overrightarrow{F}.\left(\overrightarrow{r_2}-\overrightarrow{r_1}\right)$$=\left(3\hat{\mathrm{i}}-4\hat{\mathrm{j}}+5\hat{\mathrm{k}}\right)·\left(4\hat{\mathrm{i}}-2\hat{\mathrm{j}}-1\hat{\mathrm{k}}\right)$

$=12+8-5=15 units$