Energy Smart

I have got a problem which is described below.

A heavy metal ball starts to fall from 1 meter height, ant this ball hits a light tennis-ball on the table. After the hit, metall ball rises nearly to 1 meter height. To what height does a light tennis-ball rise?

In my opinion, energy conservation law should be used here. But then it means that the tennis-ball nearly don’t rise, and as I suppose, it is not a logical answer.

Could anyone help me with this problem?

Thanks in advance.
This is a problem where masses can’t be measured.

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