set up the triangle with the information given. then just solve for x.
Purple flowers: black flowers = 4:8 = 108
4 + 8 = 12
108 / 12 = 9.
9 x 4 = 36.
36 of the flowers are purple.
So, we first add the 20 and 72 together and you will get 92.
What I like to do next is usually 92/100x8.5. The tax would be then 7.82
92 + 7.82 = 99.82 < 100
The answer is yes.