The answer is 4 thank you cards
Because- 2.55x3=7.65 then
$20.00-7.65=12.35 will be the left over change
Now she/he needs to buy more thank you cards as many she can get so
Subtract it (2.99) 4 times then you get your answer Like this (12.35-2.99=9.36) (9.36-2.99=6.37) (6.37-2.99=3.38)
(3.38-2.99=0.39) now after that she can’t buy no more so after that, I subtracted 4 times so basically the answer is 4 thank you cards that she bought