Pipelining requires all stages to be synchronized meaning, we have to make the delay of all stages equal to the maximum pipeline stage delay which here is $160$.
Time for execution of the first instruction $= (160+5) * 3 + 160 = 655$ ns ($5$ ns for intermediate registers which is not needed for the final stage).
Now, in every $165$ ns, an instruction can be completed. So,
Total time for $1000$ instructions $= 655 + 999*165 = 165.49$ microseconds
Correct Answer: $C$