Biology help (10 points)?

When a white ram is mated with black ewes it sired only white lambs. When this ram was mated with a certain white ewe all lambs were white. When one of these lambs reached maturity it was backcrossed with it's mother which produced a black lamb. Account for these results by making diagrams of each of these cross mediocre including genotypes of the parents gametes and offspring and the phenotypes of the parents and offspring