How many numbers must be selected from the set {1, 2,3,4,5,6}to guarantee that at least one pair of these numbers add up to 7

Aflower has 26 chromosomes. to create a new flower, how many chromosomes would a sperm cell have? what is this process called? part 2: within a flower cell that has 26 chromosomes, how many chromosomes would a cell that is created within the stem of a flower as it grows, have? what is this process called?