For part i, the range of the graph lies in between 3 and 9. Refer to the working for explanation. For part ii, healthy respiration rate for the boy lies between 1.52min and 3.48 min for 5 minutes. If the domain is not restricted, it means for every 5 minutes, between 2 values will be R>=7. In this case, the domain is infinite as question is asking for every 5 min(in other words for every period of the curve). Since every 5 min is the period of the curve, in other words, the length of time of healthy respiration rate for the boy for every 5 min is 1.96min(the difference between the two possible values when R>=7). Hope it helps:)