IMO, the question is unclear
The question is unclear to me. I understand we expect a triploid nucleus plus a diploid zygote (double fertilization) but I don't understand what
(TTT + TTt), TT means.
I am not so used to thinking about double fertilization in plants. In short, two pollens are involved. One fertilize a haploid gamete from the mother and the other fuse with two haploid gamete (polar nuclei) from the mother (triple fusion) resulting in a triploid "individual".
In my below answer, I am assuming that any two polar nuclei can fuse with the pollen. I am not sure this is true. If it is systematically polar nuclei resulting from the same meiosis II (that is they have the same parent cell after meiosis I), then t story is a little different.
How I understand the question
In my understanding, we are talking about a single locus with two alleles
t. Both pollens are
T. The mother is
There are two possible gametes from the female side
t. Only one possible gamete from the male side
T. Therefore, the diploid zygote is either
, where the numbers indicate probabilities
Now, for the triploid nucleus resulting from the fertilisation of two polar nucleus from the mother and one pollen grain can be either
Now, I have no idea how that matches to the possible answers as I don't understand the notation.