#### 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.

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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