Answer:
Dylan can plant maximum 8 plants.
Number of marigolds in each flower box 
Number of periwinkles in each flower box 
Step-by-step explanation:
Number of marigolds = 64
Number of periwinkles = 72
To find the maximum number of flower boxes Dylan can plant, find H.C.F of 64 and 72.

So,
H.C.F(64, 72) = 
That is Dylan can plant maximum 8 plants.
Number of marigolds in each flower box = 
Number of periwinkles in each flower box = 