Question 34422
Let the price of single roses be $X

With the money you have, you can buy

1) 7 dozen roses + 4 single roses, OR
2) 64 single roses

Since the same money can buy the roses, we can equate both 1 & 2, so

7 dozen roses + 4 singles = 64 single roses

i.e. 7 dozen roses = (64-4) singles

i.e. 7 dozens = 60 singles
 now, we know the price of a dozen ($30), so 7 dozens = $210
so, 60 singles also cost $210, thus each single costs 210/60 = $3.5

So, you have money for 7dozen roses + 4 singles
= $210 + 4 * 3.5 = $224
and each single costs $3.5