No need to guess and check....we can solve directly
Let the boxes of thank you cards = x
Let the boxes of get well cards = 8 - x
So we can solve this
4x + 6 ( 8 - x) = 36 simplify
4x + 48 - 6x = 36
-2x + 48 = 36 subtract 48 from both sides
-2x = -12 divide both sides by -2
x =6 = boxes of thank you cars
8 - 6 = 2 boxes of get well cards