The correct answer is ten.
Codominance is a form of dominance where the alleles of a gene pair are completely expressed in a heterozygous condition.
In a population of weasels, black (B) and white (W) are co-dominant traits and the heterozygous genotype produces black and white spotted weasels. It can be represented by
Parents - Black (BB) x White (WW)
Gamtes - B x W
F1 generation - BW (Black and white spottes weasles)
When, two weasles of F 1 generation (black and white spotted) are crossed with each other, the genotype of the offspring would be one black weasle (BB), two black and white spotted weasles (BW) and one white weasle (WW). If, out of the four weasles produced, one is white, then 10 white weasles are produced out of 40 weasles born.