In humans, a hypothetical trait is under the control of a single gene, A.

In humans, a hypothetical trait is under the control of a single gene, A.  Four alleles have been found:  A1, which is dominant to all others;  A2, which is dominant to A3 and A4, which are codominant.

If gene A is on an autosome, how many different genotypes are possible?

If gene A is on an autosome, how many different phenotypes are possible?

If gene A is on the X, how many different genotypes are possible?

If gene A is on the X and homozygous and hemizygous genotypes have different phenotypes, how many different phenotypes are possible?

Any help explaining these would be really appreciated! Thank you!!