Genetic crosses question ?

When a white ram was 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 thes lambs reached maturity, it was back-crossed with its mother, which produced a black lamb. Account for these results by making diagrams of each of these crosses mentioned, including the genotypes of the parents, gametes and offspring and the phenotypes of the parents and offspring. Hint: you should show three different crosses

Please show me how to do it so that I understand for my other questions which are like this one.
Thanks.