One tree produces about 2.6*10^2 = 260 lb of oxygen in 1 year.
The amazon rain-forest has about 3.9 * 10^11 trees. So each year, 3.9*10^11*260 = 10.14 * 10^13 lb of oxygen each year. One year is consisted of 365 days, so each day, (10.14*10^13)/365 = 2.77 lb of oxygen are produced each day.
Hope this Helps! :)
