Answer:
50%
Step-by-step explanation:
This is a simple one trait Punnett square.
Because we know that the recessive trait is blue (yy) thanks to the text mentioning SpongeSusie being blue and recessive. Spongebob is yellow with a genotype of Yy or heterozygous. So we need two y to make a blue baby.
Yy X yy = 50% yellow Yy and 50% blue yy