During double fertilization, one sperm fertilizes the egg forming a zygote. what does the second sperm fertilize to form, and what is its ploidy

In a process called double fertilization, one sperm fertilizes the egg, forming the zygote; the other sperm fuses with two polar nuclei in the female gametophyte, forming a triploid (3n) nucleus. The zygote develops into the plant embryo, and the triploid nucleus divides and gives rise to the endosperm.

This is giving me a headache i have asked others and they don’t know it either