|MadSci Network: Agricultural Sciences|
One of the best source of information is the Nutrient Data Laboratory of the USDA at http:// www.nal.usda.gov/fnic/foodcomp.
Browsing there, I was able to find those vitamin C values (mg per cup):
Sunny Delight: Not available
Please note that these values may depend on the kind of juice: fresh, made from concentrated with vitamin C added or not, etc.
An interesting experiment to do in school is to measure the content of vitamin C yourself. There are many well written methods on the web, including this one:
Try the links in the MadSci Library for more information on Agricultural Sciences.