Answer:
100%
Step-by-step explanation:
Yellow flower color (Y) is dominant over white flower color (y). Plant A is YY while plant B is yy:
YY x yy
Yy Yy Yy Yy
All the offspring would have Yy genotype and since Y is dominant over y, all of them will have yellow flower color as opposed to while.
Hence, the percentage of the offspring that will have a yellow flower would be 100%.