If Mary sold $192 worth of greeting cards and received a 25% commission on her sale, we can find her commission by multiplying the sale amount by the commission rate expressed as a decimal:
Commission = Sale amount * Commission rate
where the commission rate is 25% or 0.25
So, Mary's commission is:
Commission = $192 * 0.25 = $48
Therefore, Mary earned a commission of $48 on her sale of $192 worth of greeting cards.