For the formation of a single wheat grain we require 80 egg cells and 80 pollen grains. Usually, a single functional egg cell is formed at the end of meiosis. Therefore, for the formation of 80 egg cells there should be 80 meiotic division.
Single meiotic division in microspore mother cell produces 4 functional pollen grain. Thus, produce 80 pollen grains the total number of meiotic division would be 20.
Therefore, in all, there will be 100 meiotic division, 80 for egg cells and 20 division for pollen grain to produce 80 wheat grains.