You should help your sister out whenever possible.
Frank is at home relaxing when his sister Martha calls him to ask him to watch her kids while she goes out.
Frank wants to respond to his sister's request for babysitting.
Frank tells his sister that he'll be over right after he gets ready.
Frank tells his sister that he's relaxing now, so he's not able to come over and help.
Martha is relieved she'll get a babysitter for her kids and is happy she can count on Frank.
Martha is annoyed that Frank is too lazy to come help her when she needs him.