Figure the fraction of box tops each class collected, then multiply the prize money by that fraction.
Total box tops = 3760 +2301 +1855 = 7916
Mr Coronado's class's fraction: 3760/7916 × $600 = $284.99
Mrs De Souza's class's fraction: 2301/7916 × $600 = $174.41
Mr Nost's class's fraction: 1855/7916 × $600 = $140.60