Are you looking at blood types?
If one Parent is AB and another is A?, the A? has to be AA or AO.
So the gametes would be A or B for the AB parent
And A or A for the second parent if the ? is A
But if ? is O, the the second would be A and O.
The cross would be 1:1 AA and AB if the ? is A.
The cross would be AA, AO,AB, BO if the? is O
If ? is A:
A A
A AA AA
B AB AB
or if ? is O:
A O
A AA AO
B AB BO