How many chromosomes would be found in an allotetraploid plant if its parent species had diploid numbers of 4 and 6 respectively?

An allotetraploid plant has its chromosomes derived from two different plants (different chromosomes) and it has 4 chromosomes of each type of chromosome because it received two copies of each chromosome and doubled it. So, this plant, would have 20 chromosomes. (4+6) * 2=20

4 - > 2n of one parent

6 - > 2n of the other parent

2 times because it is a "tetraploid" plant and it already has 2 copies of each of its parents chromosomes.