Jack is married to Jill. They have two children, Mark and Julie. Mark is married to Sandra, who is an only child. Julie's husband, Alex, has one sister named Angela. How is Angela related to Sandra, and how is Jill related to Alex? Make your response very short.
Angela is the sister of Alex, who is married to Julie. Since Julie and Mark are siblings, Sandra, being Mark's wife, is Julie's sister-in-law. Therefore, Angela, as the sister of Alex, is unrelated by blood to Sandra but can be considered the sister-in-law of Alex's sister-in-law, which is Sandra.

Jill is the mother of Julie, and Alex is married to Julie, making Jill Alex's mother-in-law. Hence, Jill is Alex's mother-in-law, and Alex is her son-in-law.