What is the greatest number of identical bouquets that can

Look for the factors of 21 and 91:

white = 21 = 3 x 7
red = 91 = 13 x 7

The common factor is 7, thus the greatest number of identical bouquets is 7.

Let me explain graphically:

_______Identical Bouquets (7 bouquets)______________
\(\;\;\;\;\;\;\)White \(\;\;\;\;\) Red
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips
\(\;\;\;\;\)3 tulips\(\;\;\;\;\) 13 tulips = 3 white and 13 red tulips