So, since the trait is eye color, let's use E to represent the dominant allele (brown) and e to represent the recessive allele (blue).
I've attached a Punnett square, but let me real quick explain how I set it up. We know that both parents are heterozygous, which means that they have one of each allele. So that gave us the two sides. Then I filled in the boxes (I assume you've leaned how to do this, if message me and I can explain it).
Looking at the results we can see that 1/4 of the offspring are EE, 1/2 are Ee, and 1/4 are ee. Since the blue allele (e) is recessive, it'll only be expressed if no dominant brown alleles (E) are present. Therefore, only the ee genotype will exhibit blue eyes. So, 1/4 or 25% of the offspring will have blue eyes.
Hope that helps! If you need clarification or anything feel free to message me :)
