I have included a graph to help you see what the domain and range would be There are no minus y values. 0<y< infinity y is included in the reals. The domain is - infinity < x < infinity.
I don't want to say that either x or y can equal - or + infinity. Some teachers allow it. You have to ask your instructor what they will accept.
So A = the child is 5-10 years old and B = the child is 11-13 years of age and that covers all the children in the study. I = calcium intake is inadequate.