This is a question of randomness so there really is no answer. I would guess 7 since that is the center page and you're more likely to open it up in or near the middle
6f = x
x stands for how many flowers the parade can use
The easiest way is to use (& to memorize) the sum formula for a AP:
Sum = 1st term added to the last term & multiplied by half the number of terms
S = (a+l)n/2
S = (5 + 53)(7/2) = 203
