If a woman is heterozygous for type a and her husband is heterozygous for type b what is the probability of blood types that their offspring would have

For this you would use a punnet square (ill try my best to show it while typing)

heterozygous means different, so (with blood type) with heterozygous A you will see AO (this will be blood type A)

A O

B AB BO

O AO OO

you then have the types in the squares:

AB (type AB blood)

BO (type B blood)

AO (type A blood)

OO (type O blood)