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Answer :

In this case we have

[tex]D(t)=10\sin (\frac{t}{20})+10[/tex]

In this case we will graph the function

As we can see the lowest point is on 30 pi

[tex]D(30\pi)=10\sin (\frac{30\pi}{20})+10=10(-1)+10=-10+10=0[/tex]

ANSWER

30pi seconds

View image QuintS711039