We know that H is for dark hair color, and h is for clear or light hair color.
Considering this, the exercise tells us the parents are Hh the mother, and hh the father, and to tell the probabilities of each genotype in the offspring, which can be represented with a Punnet square, as follows.
Here we can appreciate how the offspring of the couple would have a 75 % to have dark hair color, while 25 % of the offspring would have light hair color.