question baout metro card - 紐約

I am wondering does the monthly metrocard card ($81) cover bus riders as well?

Someone told me that if I take the subway, and I will be able to ride buses
within 2 hrs. Does that work other way around?

Also, does anyone know what's the different between the $81 and $101?
metro card?

I am just so confused right now.

If someone can tell me, it would be great.

Thanks all.

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