Answer: Bb/bb (let's take letter B this time, just for no reason since it does not matter :) )
Explanation:
if the ryan's genotype is Bb, alexa's genoype is BB, then the genotype ryan's biological father is either Bb, or bb
punnet square evidence (option 1):
B b
B BB Bb
B BB Bb
punnet square evidence (option 2):
b b
B Bb Bb
B Bb Bb