Achild takes a nap averaging three hours and gets an average of 12 hours of sleep at night. nap time and night time sleep can each vary by 30 minutes. what are the possible lengths for the child's nap and night time sleep

Since nap time averages 3 hrs and can vary by 30mins then nap time = 3 + 0.25
since night time sleep averages 12hrs and van vary by 30 minutes then night time sleep = 12+ 0.25
minimum nap and night time sleep = 2.75+ 11.75=14.5hrs
max nap and night time sleep= 3.25+12.2= 15.5hrs
nap and night time sleep = 15+ 0.5 hrs 
total sleep time averages 15hrs and can vary by 1 hr (1/2 hr above or below 15 hrs) 
hope this helped if not I'm sorry