Answer: 25%, or 1/4
Step-by-step explanation:
We are assuming that the albinism trait is recessive, or that two of the albinism alleles are required for a person to develop albinism. Because the parents do not have albinism, we can assume that they have at least one dominant allele (A). Since they have a child with albinism, we can also assume that they both have at least one recessive allele (a), or that they are heterozygous carriers of the trait (Aa).
Punnet Square:
A a
A AA Aa
a Aa aa
From this cross, we can see that these particular parents have a 25% chance (1/4) of having a child with albinism (this is the probability of any of their children, including the next). Already having a child with albinism does not affect this probability.