Answer:
For you to answer to this question you need to think at the alleles, so let's say the dominant one is A, and the other one is a.
Step-by-step explanation:
With that said, we need to take a look at a proportion below:
Let's imagine the possibility of both flowers being Aa, so we have Aa x Aa right? Okay, now let's do the math
AA Aa Aa aa
Now it's time for us to check the information to see if it matches with the question, we have 600 blue to 200 red flowers, that means 3/1 because: 600/200 = 3/1. So for each red we'll have 3 blue flowers. So this is correct, but we still need the answer, how many of them are heterozygous, well, if this is the right path to follow, it'll be like this:
AA Aa Aa (not counting the aa because they're red)
These are the blue ones, but we need the heterozygous right? so the relationship will be like: for each AA we'll have 2 Aa, doing the math the answer will be 400.