Doesn't look correct to me.

let i = number of flowers

r = number of fruits

P(B) = summation from i = r to infinity {P(r|i).P(i)}

P(A.B) = P(B|A).P(A)

P(A) = Probabiltiy there were 'n' flowers - which is straight fwd

P(B|A) = nCr

Try to put these values and simplify