Answer
$11.8$
Work Step by Step
If $\overrightarrow {r}$ is the sum of two vectors $\overrightarrow
{r}=\overrightarrow {c}+\overrightarrow {d}$,
then $\Rightarrow$
$ r_{x}=c_x+d_x;$
$r_y=c_y+d_y;$
$r_{z}=c_{z}+d_{z}$
So we get,
$r_{x}=c_{x}+d_x=7.4+4.4=11.8$
