Answer:
0.15 = 15%
Step-by-step explanation:
Let's call the recessive allele x, and the dominant allele X.
The homozygotes have the pair xx, and the heterozygotes have the pair Xx.
If two heterozygotes conceive a child, there are four configurations that the child can have:
xx, xX, Xx, XX
the only configuration that allows the child the possibility to have extra fingers and toes is the xx, as this aspect is a recessive trait, so the probability of the child being xx is 25% (1 option between 4 options, all of them with equal probabilities).
If the child is xx, there is a chance of 60% of the child having extra fingers and toes. So, the final probability is:
25% * 60* = 0.25 * 0.6 = 0.15 = 15%
and 
. Then
(the part of the sphere above the cone) is given by