Wavy hair in humans is a result of incomplete dominance between straight hair (h) and curly hair (h). if a man with curly hair marries a woman with wavy hair, will any of their children have straight hair?

As mentioned in the question, wavy hair is a result of phenomenon of incomplete dominance where no allele is dominant over the other.

So if we say a man with curly hair (hh) marries a woman with straight hair (HH), we need to find out will their kids have straight hair or not.

Let us cross them:

Parents:                                      hh X HH

Gametes:                                    h : h and H :H

Offspring:                                hh: Hh: hH: HH

Probability of children with straight hair (HH) = 25 %

Probability of children with curly hair (hh)  =      25%

Probability of children with wavy hair =              50 %

So there is a chance of 25 % that their kids can have straight hair.

Hope it helps!