The minimum donation for one card is $18.
The minimum donation for two cards is $36.
The minimum donation for three cards is $54.
The minimum donation for four cards is $72.
The minimum donation for five cards is $90.
The minimum donation for six cards is $108.
The minimum donation for seven cards is $126.
The minimum donation for eight cards is $144.
The minimum donation for nine cards is $162.
The minimum donation for ten cards is $180.