Answer
$0.9$
Work Step by Step
We know that $\sin$ has a period of $2\pi$, hence $\sin(\theta)=\sin(\theta+2k\pi)$ where $k$ is an integer.
Therefore,
$\sin(\theta)+\sin(\theta+2\pi)+\sin(\theta+4\pi)\\
=\sin(\theta)+\sin(\theta)+\sin(\theta)\\
=0.3+0.3+0.3\\
=0.9$