How’d u do this i am very confused

Hey there! :)

To solve a Punnett square, we need to master the fields in the attached picture

In the question, the given keys are:
Dominant allele Y → yellow
Recessive allele y → green

                    Y      |       y

      Y     |    YY            Yy

      Y     |    YY            Yy

This would be the Punnett square for this question
  
Percentage of offspring to have yellow seeds?

Yellow is Y, then we should count which alleles had YY as a genotype?

YY = 2 out of 4, then 50%

The answer is a: the eggs have half as many chromosomes as the body cells