#### Answer

We can estimate that the period is 20 years.

#### Work Step by Step

We can see that the graphs seem to repeat similar shapes every 20 years approximately.
Therefore, we can estimate that the period is 20 years.

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Published by
Pearson

ISBN 10:
978-0-13-421743-7

ISBN 13:
978-0-13421-743-7

We can estimate that the period is 20 years.

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